In a medium size skillet, heat oil on medium heat.
Add onion to a pan and cook 2-3 minutes, until translucent. Stir in the shredded chicken, taco seasoning, drained tomatoes, and drained green chiles. Stir to combine. Reduce heat to low and allow to simmer for 5-8 minutes.
Arrange the taco shells in prepared baking dish, standing up. Warm the taco shells in the oven for about 2-3 minutes. Remove from oven. Spoon and spread 1 tbsp of refried beans into the bottom of each shell. Top with chicken mixture, leaving a little room for taco toppings.
Sprinkle each taco generously with cheese.
Bake for 7-10 minutes, until the cheese is melted and the shells are just starting to brown.
Remove from the oven and top with your favorite taco toppings and a squeeze of lime.