Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper or aluminum foil for easy cleanup.

In a large skillet over medium heat, cook the ground beef until browned and fully cooked, breaking it into crumbles as you go. Drain any excess grease.

Add the taco seasoning and water to the skillet with the cooked ground beef. Stir well and simmer for 3-4 minutes until the mixture thickens slightly.

Place the taco shells on the prepared baking sheet and fill each shell with a generous spoonful of the seasoned ground beef mixture.

Sprinkle shredded cheddar cheese evenly over the ground beef in each taco shell.

Bake in the preheated oven for 8-10 minutes, or until the cheese is melted and the taco shells are crispy.

Carefully remove the tacos from the oven and let them cool for 1-2 minutes.

Top each taco with diced tomatoes, shredded lettuce, and cilantro, if desired.

Serve warm with sour cream on the side for dipping or topping.