Preheat your oven to 375°F (190°C). Generously grease 8 cups of a standard metal muffin pan with non-stick cooking spray.
If your tortillas are large, use a wide cutter or glass rim to cut them into smaller 4-inch circles. Warm them slightly in the microwave so they are pliable, then press one into each greased muffin cup to form a bowl.
Bake the empty tortilla cups for 5-7 minutes until lightly golden and firm. Remove and set aside.
In a large skillet over medium heat, brown the ground beef, breaking it up with a stainless steel spatula. Drain any excess grease.
Add the taco seasoning packet and the water to the beef. Stir well and simmer for 3-4 minutes until the sauce thickens.
Spoon the hot seasoned beef evenly into the pre-baked tortilla cups. Sprinkle the shredded cheddar cheese generously over the top of the meat.
Return the muffin pan to the oven and bake for another 5-7 minutes until the cheese is completely melted and the tortilla edges are crispy.
Remove from the oven. Top each cup with shredded lettuce, diced tomatoes, a dollop of sour cream, and fresh cilantro. Serve immediately!