Prep the peppers: Preheat the oven to 375°F (190°C).
Slice the tops off the bell peppers and remove seeds and membranes. If they don’t stand upright, trim a thin slice from the bottoms to steady them. Place them cut-side up in a baking dish.
Par-cook (optional but helpful): Brush the pepper interiors with a little olive oil and sprinkle with a pinch of salt.
Cover the dish loosely with foil and bake for 10 minutes to soften. This helps ensure tender peppers.
Sauté aromatics: Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the chopped onion and cook 3–4 minutes until translucent.
Stir in the garlic and cook 30 seconds until fragrant.
Brown the meat: Add the ground beef or turkey. Cook, breaking it up with a spoon, until browned and no longer pink, 5–7 minutes. Drain excess fat if needed.
Season and sauce: Stir in taco seasoning, salt, and pepper.
Add salsa and tomato sauce. Simmer 2–3 minutes until slightly thickened and saucy.
Stir in mix-ins: Fold in the cooked rice, black beans, and corn if using. Taste and adjust seasoning with more salt, pepper, or taco seasoning.
Remove from heat and stir in 1/2 to 3/4 cup of the shredded cheese.
Stuff the peppers: Spoon the filling into each pepper, mounding slightly. Top with the remaining cheese.
Bake: Cover loosely with foil and bake 15 minutes. Remove foil and bake another 10–12 minutes, until the peppers are tender and the cheese is melted and lightly golden.
Garnish and serve: Let rest 5 minutes.
Sprinkle with cilantro or green onions. Serve with sour cream, avocado, and lime wedges for brightness.