Cheese & Onion Enchilada Casserole

1 dozen corn tortillas (thaw if frozen)
2 cans Old El Paso "medium" or "hot" enchilada sauce (red)
1/2 cup chopped onion
4 cups shredded cheese
oil

Bring one can of enchilada sauce to simmer in a saucepan. Heat oil in a skillet (not too hot). Place tortillas, one at a time, in skillet - frying lightly on each side. Drain each on paper towels. Place fried tortilla in simmering sauce briefly to coat with sauce. Remove coated tortilla to work area/cutting board and put a few onion pieces and cheese to suit on the flat tortilla. Roll the tortilla (messy) and place in an oblong casserole dish. Repeat process for each tortilla. Sprinkle remaining cheese on top. Pour remaining enchilada sauce over top of casserole - open second can if necessary. Place in oven at 350 for approx 10 minutes - until cheese is melted..