Brown the beef in a skillet (6–8 mins), add onion (cook 3–4 mins), then garlic (1 min). Stir in taco seasoning with ¼ cup water and simmer until thick (5 mins). Season to taste.
Melt butter, whisk in flour, and cook 1 min. Slowly add milk and simmer. Add cream cheese, then stir in cheddar, Monterey Jack, diced bell pepper, tomatoes, cilantro, and spices. Keep warm.
Bake taco shells at 375°F for 3–5 mins until crisp.
Fill each shell with beef, spoon over cheese sauce, sprinkle more cheese, and bake 2–3 mins until bubbly.
Top with cilantro. Serve hot with sour cream and hot sauce.