Preheat oven to 325°.

Heat 1 tablespoon olive oil in skillet. Add onion and cook until lightly browned. Pulse tomatoes in a blender, then add to skillet, along with taco seasoning mix and can chiles. Simmer 15 minutes.

In greased casserole dish, layer tortilla chips, tomato mixture and cheese. Top with sour cream.

Bake at 325° for 30 minutes.