Preheat your oven to 375°F (190°C). Lightly grease a muffin tin with cooking spray.
In a skillet over medium heat, cook the ground beef until browned. Drain any excess fat.
Add the taco seasoning and water to the skillet. Stir well and simmer for about 5 minutes, until the mixture thickens.
While the beef is cooking, gently press a wonton wrapper into each muffin tin cup to form a shell.
Fill each wonton shell with a spoonful of the beef mixture, then top with shredded cheddar cheese.
Bake in the preheated oven for 12-15 minutes, or until the wonton wrappers are golden brown and the cheese is melted.
Remove from the oven and let cool for a few minutes. Carefully remove the taco cups from the muffin tin.
Top each taco cup with diced tomatoes, shredded lettuce, and a dollop of sour cream. Add any optional toppings as desired.