Preheat oven to 350 degrees.
Saute onion in vegetable oil in a skillet.
Add chicken, green chiles, diced tomatoes, mix and heat to just boiling over medium heat.
Spread a thin layer of refried beans on each tortilla.
Pour a thin layer of enchilada sauce on the bottom of the 9x13 pyrex dish
Fill each tortilla with chicken filling mixture.
Sprinkle some shredded cheddar cheese inside each filled tortilla.
Fold / roll and arrange closely together in the 9x13 pyrex baking dish.
When 9x13 is filled with stuffed tortillas, pour more enchilada sauce over all of the tortillas.
Top with more cheddar cheese.
Cover with foil, bake for 45 minutes.
Serve and enjoy! Optionally top with shredded lettuce and sour cream.