Heat oven to 400°F (200°C). Slice tops off peppers, remove seeds and membranes, chop usable pepper tops, and stand peppers in a baking dish.

Brown ground beef in a skillet over medium-high heat, about 5 minutes. Add onion and chopped pepper tops, cook 3 minutes. Stir in garlic and cook 30 seconds.

Off heat, stir in taco seasoning, rice, tomato sauce, and water until evenly mixed.

Fill peppers with the mixture and pour ¼ cup water into the dish. Cover tightly with foil and bake 25 minutes, until peppers are tender.

Uncover, top with cheese, and bake uncovered 5 to 7 minutes until melted and bubbly. Let rest 5 minutes, then serve with sour cream, cilantro, and avocado.