Preheat oven to 350 degrees F.

Cook ground beef and onion in a large skillet until meat is browned and onions are teneder; then drain. Stir in refried beans, salt, and pepper; stir well. Cook meat mixture over low heat for 10 minutes. Heat oil in a small skillet over medium heat until a drop of water instantly vaporizes when placed in the pan. Using tongs, quickly dip corn tortillas in the oil until soft, about 15 to 20 seconds (don't allow them to become crisp). Place cooked tortillas on absorbent towels to drain. Spoon about 1/3 cup meat mixture onto each tortilla, top with some tomatoes and roll up tightly. Place rolled tortillas, seam down, in a lightly greased 9- by 13-inch baking dish. Pour cheese sauce over top. Bake in a 350 degree F oven until hot and bubbly, about 20 to 25 minutes. Garnish with sliced ripe olives, if desired.

To make cheese sauce:

Melt butter in a medium sauce pan, blend in flour and seasonings. Cook over low heat till smooth and bubbly. Remove from heat. Stir in milk and enchilada sauce. Return to heat and bring to a boil. Add olives, pepper sauce and cheese. Stir until cheese melts.