Preheat your oven to 400 °F. This ensures the taco shells will crisp properly. In a skillet, heat the olive oil over medium heat until shimmering. Add diced onion and cook for a few minutes until it turns translucent and fragrant. This base builds depth of flavor.
Add shredded chicken, taco seasoning, drained tomatoes, and green chiles to the skillet. Stir to coat everything evenly. Let it simmer for about 5–8 minutes so flavors meld and excess moisture evaporates. A good simmer helps ensure the filling isn’t watery.
Arrange taco shells standing upright in the baking dish (you should fit about 10). Bake them empty for 5 minutes – this pre-crisping method ensures the shells stay crunchy even after baking with filling.
Remove shells from the oven. Into each, spoon about a tablespoon of refried beans on the bottom – this acts as a glue and barrier. Press the bean layer flat, then fill the shell almost to the top with the chicken mixture. Generously sprinkle freshly shredded Mexican cheese over each taco. Once filled, bake again for about 7–10 minutes, or until cheese melts and shell edges become golden.
Take the tacos out once cheese is bubbly and edges are browned. Let them cool a minute, then top with your favorite extras – sour cream, jalapeños, salsa, fresh cilantro, or shredded lettuce. Serve immediately for peak crispness and flavor.