1. Prepare the Bell Peppers:
* Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish or line it with parchment paper.
* Wash the bell peppers thoroughly. Slice them in half lengthwise, from stem to bottom.
* Carefully remove the seeds and white membranes from each pepper half. You want a clean cavity for the filling. If the pepper halves don’t sit flat, you can shave a tiny sliver off the rounded bottom to create a stable base, being careful not to cut through.
* Optional Par-Baking: For softer peppers, you can par-bake them. Place the pepper halves cut-side down in the prepared baking dish, add about ¼ inch of water to the bottom of the dish, and bake for 15-20 minutes. This pre-softens them and reduces overall baking time later. Remove from oven, discard water, and set aside. If you prefer firmer peppers, you can skip this step.

2. Cook the Quinoa:
* Rinse the 1 cup of uncooked quinoa thoroughly in a fine-mesh sieve under cold running water. This step is crucial to remove saponins, a natural coating that can make quinoa taste bitter.
* In a medium saucepan, combine the rinsed quinoa and 2 cups of vegetable broth (or water). Bring to a boil over medium-high heat.
* Once boiling, reduce the heat to low, cover the saucepan, and let it simmer for about 15 minutes, or until all the liquid has been absorbed and the quinoa is fluffy. You’ll see tiny spirals (the germ) separating from the seeds.
* Remove from heat and let it stand, covered, for 5 minutes. Then, fluff the quinoa with a fork. Set aside. You should have about 3 cups of cooked quinoa.

3. Prepare the Aromatic Base for the Filling:
* While the quinoa is cooking (or after), heat 2 tablespoons of olive oil in a large skillet or Dutch oven over medium heat.
* Add the finely chopped yellow onion and sauté for 5-7 minutes, until softened and translucent, stirring occasionally.
* Add the minced garlic and cook for another 1-2 minutes until fragrant. Be careful not to burn the garlic, as it can become bitter.

4. Build the Flavorful Filling:
* To the skillet with the onions and garlic, add the rinsed and drained black beans and the corn (if frozen, no need to thaw). Stir to combine.
* Stir in the can of undrained diced tomatoes. The liquid from the tomatoes helps create a saucy consistency for the filling.
* Add the spices: chili powder, ground cumin, smoked paprika, dried oregano, salt, and black pepper. Stir well to ensure everything is evenly coated and the spices become fragrant, cooking for about 2-3 minutes.
* Taste the filling at this point and adjust seasonings if necessary. You might want more salt, a bit more chili powder for heat, or a pinch of sugar if your tomatoes are particularly acidic.

5. Combine Quinoa and Filling:
* Add the cooked, fluffed quinoa to the skillet with the vegetable and spice mixture.
* Stir gently but thoroughly to combine everything. Ensure the quinoa is well-integrated with the other ingredients, creating a cohesive and flavorful stuffing.
* Stir in about half of the chopped fresh cilantro or parsley, reserving the rest for garnish.

6. Stuff the Bell Peppers:
* Carefully spoon the quinoa filling mixture generously into each bell pepper half. Pack it in gently but don’t compress it too much. You want the filling to be substantial.
* Arrange the stuffed pepper halves, cut-side up, in the prepared baking dish. They should fit snugly but not be overcrowded. If they wobble, you can use scrunched-up foil to prop them up.

7. Bake the Stuffed Peppers:
* If you didn’t par-bake the peppers, you might want to add about ¼ cup of water or vegetable broth to the bottom of the baking dish. This creates steam and helps the peppers cook through without drying out.
* Cover the baking dish loosely with aluminum foil. This prevents the tops of the filling from drying out or burning before the peppers are tender.
* Bake in the preheated 375°F (190°C) oven for 25-30 minutes if you par-baked the peppers, or 40-50 minutes if you started with raw peppers. The peppers should be tender when pierced with a fork, and the filling should be heated through.

8. Add Cheese (Optional) and Final Bake:
* If using cheese, remove the foil from the baking dish. Sprinkle the shredded cheese evenly over the top of each stuffed pepper.
* Return the dish to the oven, uncovered, and bake for another 5-10 minutes, or until the cheese is melted, bubbly, and slightly golden.
* If you prefer a crispier top without cheese, you can skip the cheese and broil for the last 1-2 minutes, watching carefully to prevent burning.

9. Rest and Garnish:
* Once baked to perfection, carefully remove the baking dish from the oven. Let the stuffed peppers rest for 5-10 minutes before serving. This allows the flavors to meld further and makes them easier to handle.
* Garnish generously with the remaining fresh cilantro or parsley.