Preheat your oven to 375°F (190°C) while you prepare the filling.

In a skillet over medium heat, heat olive oil and add the diced onion and minced garlic. Sauté until fragrant. Add the ground beef, breaking it apart as it cooks. Once browned, stir in taco seasoning and tomato sauce along with salt and pepper to taste. Let simmer for about five minutes.

Fill each taco shell generously with the meat mixture. Sprinkle each filled shell with shredded cheese before placing them standing side by side in a lightly greased baking dish.

Place your baking dish in the preheated oven and bake for about 10–15 minutes until bubbly and slightly crispy.

Remove from the oven and top each taco with shredded lettuce, diced tomatoes, red onion, and fresh cilantro. Add optional toppings like sour cream or guacamole if desired.