Preheat oven to 400°F and line a sheet pan with foil.
Arrange bell pepper slices on the sheet pan and set aside.
In a large skillet over medium heat, cook the ground beef until it begins to crumble and brown, draining any excess liquid. Add garlic, chili powder, cumin, oregano, onion powder and salt, and cook until meat is browned. Stir in the salsa and cook for 5 more minutes until heated through.
Spoon the ground beef mixture evenly onto the peppers, making sure to cover each one, then sprinkle with shredded cheese.
Bake for 10 to 12 minutes, until peppers are tender and cheese is melted. Remove from oven and add optional toppings if desired.