In a large skillet, heat the olive oil over medium-high heat. Add the diced onion and sauté for about 3 minutes until it becomes translucent.

Add the minced garlic and cook for an additional minute, until fragrant.

Increase the heat to high and add your chosen protein to the skillet. Cook for about 5-7 minutes, breaking it down with a spatula, until browned and cooked through.

Sprinkle the taco seasoning over the protein, along with the diced tomatoes. Stir everything together and let it simmer for 3-5 minutes, until the mixture is heated through and flavors meld.

Taste and adjust seasoning with salt and pepper as needed.

Load the taco shells with the flavorful mixture and add your desired toppings.