In a large pan, brown ground beef & onions; drain. Return to pan, add taco seasonings & water, bring to a boil and then simmer for 8-10 minutes. Stirring occasionally.
Pre-heat oven to 375 degrees. In the meantime, mix refried beans and sour cream, set aside.
In A 9x13 in. deep Pan, spray with a non-stick cooking spray. Spread 1/2 cup of enchilada sauce on to bottom of pan.
In a shallow medium size bowl, pour 1/2 a can of enchilada sauce. This will be used to dip and coat both sides of corn tortillas, using 6 tortillas per layer.
Assemble & coat 6 corn tortillas, line on the bottom of pan, they will over lap. On top of 1st layer of tortillas, using a slotted spoon, spoon 1/2 of meat mixture evenly, sprinkle with 1 cup of cheese. Repeat a layer of 6 enchilada coated tortillas. 2nd layer, spread out refried bean mixture evenly, sprinkle 1 cup of cheese. Repeat with a layer of 6 enchilada coated tortillas. 3rd layer, top with 2nd 1/2 of meat mixture,. Sprinkle with 1 cups of cheese. Repeat with the last 6 enchilada coated tortillas. Spread 2nd 1/2 of canned enchilada sauce over dish and top with remaining cheese and black olives.
Cover loosely with foil & baked in pre-heated 375 degree oven for 40 minutes. Remove foil and continue baking for 10 minutes or until cheese is melted & lightly golden brown.