Step 1: Preheat your oven to 375°F (190°C).
Step 2: Wash the bell peppers and slice the tops off. Remove the seeds and membranes carefully. Set aside.
Step 3: In a large skillet, heat the olive oil over medium heat. Add chopped onion and minced garlic, sautéing until translucent, about 5 minutes.
Step 4: Add the lean ground beef, breaking it apart. Cook until browned, about 7-10 minutes.
Step 5: Stir in tomato paste, fire-roasted tomatoes, parsley, oregano, basil, red pepper flakes, and Worcestershire sauce. Simmer for about 5 minutes.
Step 6: Fold in cheddar cheese cubes until well combined.
Step 7: Spoon the filling into each pepper, packing it tightly. Arrange in a baking dish.
Step 8: Cover with aluminum foil and bake for 25 minutes. Remove foil and bake for an additional 10-15 minutes until peppers are tender and cheese is bubbling.