Rinse the quinoa thoroughly under cool running water. Combine it with the vegetable broth in a saucepan, bring to a boil, cover, reduce the heat, and simmer for about 15 minutes until the liquid is absorbed; rest covered for 5 minutes, then fluff with a fork.

Heat the oven to 375°F (190°C). Slice the bell peppers in half lengthwise and remove the seeds and membranes; for softer peppers, place them cut-side up in a baking dish with about 1/4 inch of water, cover with foil, and bake for 10–15 minutes, then drain.

Heat the olive oil in a skillet over medium heat. Cook the onion for 4–5 minutes until softened, then add the garlic and optional jalapeño and cook for 30–60 seconds.

Stir in the black beans, corn, diced tomatoes, salsa, cumin, chili powder, smoked paprika, oregano, salt, and pepper. Cook for 3–5 minutes so the vegetables warm through and the seasonings mingle.

Fold the cooked quinoa into the vegetable mixture. Taste carefully and adjust the salt, pepper, or salsa before filling the peppers.

Spoon the filling into the pepper halves and arrange them in a lightly greased baking dish. Cover the dish with foil and bake at 375°F for 15 minutes.

Remove the foil and sprinkle the shredded cheese over the filled peppers. Bake for another 8–10 minutes, until the peppers are tender and the cheese is melted.

Garnish the baked peppers with chopped cilantro and serve with lime wedges. Add extra salsa, avocado, diced green chiles, or sour cream at the table if desired.