Preheat your oven to 400°F (204°C). Spray a 9×13-inch baking dish with nonstick spray.
Cook the Onion and Chicken Mixture:
Heat the olive oil in a medium skillet over medium heat. Add the diced onion and sauté for 2-3 minutes until translucent and fragrant.
Stir in the shredded chicken, taco seasoning, drained diced tomatoes, and drained green chiles. Mix thoroughly to combine all ingredients. Reduce heat to simmer and let it cook for 5-8 minutes, allowing the flavors to meld.
Prepare Taco Shells:
Place the taco shells standing up in the prepared baking dish. It’s possible to fit 10 taco shells by arranging them snugly and adding 2 on each side.
Bake the empty taco shells in the oven for 5 minutes to crisp them up slightly. Remove from the oven afterward.
Assemble the Tacos:
