Prepare the Peppers: Preheat oven to 375°F (190°C). Cut bell peppers in half lengthwise, remove seeds and membranes.
Sauté Aromatics: Heat olive oil in a large skillet over medium heat. Add chopped onion and cook until softened, about 5 minutes. Add minced garlic and cook for another minute until fragrant.
Brown the Meat: Add the ground beef, turkey, or vegetarian substitute to the skillet and cook, breaking it up with a spoon, until browned. Drain any excess grease.
Add Seasoning and Beans: Stir in the taco seasoning, black beans, and diced tomatoes (undrained). Bring to a simmer and cook for 5-7 minutes, stirring occasionally, until the sauce has thickened slightly.
Stuff the Peppers: Place the bell pepper halves cut-side up in a baking dish. Spoon the taco meat filling into each pepper half, filling them generously.
Top with Cheese: Sprinkle the shredded cheese over the filling in each pepper.
Bake: Bake in the preheated oven for 20-25 minutes, or until the peppers are tender and the cheese is melted and bubbly.
Add Toppings and Serve: Remove from oven and let cool slightly. Top with your favorite toppings, such as sour cream, salsa, guacamole, lettuce, cilantro, and lime wedges. Serve warm.