Preheat the oven to 400°F (200°C). Arrange the hard taco shells in a baking dish.

In a skillet over medium heat, cook the ground beef and diced onion until the beef is browned, breaking it up as it cooks.

Drain excess fat from the skillet. Add the minced garlic and taco seasoning, stirring for about 1 minute until fragrant.

Pour in the tomato sauce or salsa. Lower the heat and let it simmer for 4 to 5 minutes.

Carefully fill each taco shell with the beef mixture, then generously top with shredded cheese.

Place the baking dish in the preheated oven. Bake for 10 to 15 minutes or until the cheese has melted and the taco shells are golden.

Once out of the oven, add your desired toppings: lettuce, diced tomatoes, red onion, and cilantro for freshness.

Serve warm with sides like sour cream or guacamole for extra flavor.