Preheat your oven to 375°F (190°C).
In a large skillet over medium heat, add 1 lb ground beef (or chicken) and cook until browned, about 6-8 minutes. Break it apart with a spoon to ensure even cooking.
Add the finely chopped onion (1 small onion) and minced garlic (2 cloves) to the skillet. Sauté until the onion becomes translucent, about 3-4 minutes.
Stir in the taco seasoning (1 packet) and water (1/2 cup). Allow the mixture to simmer for about 5 minutes until the sauce thickens slightly.
While the meat mixture is cooking, prepare the taco shells or tortilla cups. Arrange them in a muffin tin to hold their shape.
Once the meat is ready, begin layering. Start by spreading about 1 tablespoon of refried beans (1 can) in the bottom of each taco shell.
Add a generous spoonful of the seasoned meat mixture on top of the beans.
Sprinkle a layer of shredded cheddar cheese (2 cups) over the meat in each cupcake.
Bake in the preheated oven for about 10-12 minutes, or until the cheese is melted and bubbly and the taco shell is crispy.
Remove from the oven and let cool for a couple of minutes. Carefully remove the Taco Cupcakes from the muffin tin.
Top each cupcake with salsa (1 cup), sour cream (1/2 cup), shredded lettuce (1 cup), and diced tomatoes (1 medium tomato). Garnish with chopped cilantro (1/4 cup) if desired.