Cook the 1 cup chopped onion and garlic in oil until onion is tender but not brown; stir in flour.
Add undrained tomatoes, tomato sauce, chili peppers, sugar, cumin and salt.
Cook and stir until thickened and bubbly; set aside.
Combine chicken, HALF the cheese, the 1/4 cup onion, chopped olives and the 3/4 teaspoon salt.
In skillet, dip tortillas briefly in small amount of hot oil until limp but not crisp; drain (you can also soften instead in microwave for a few seconds.) Spoon 1/4 cup of the chicken mixture onto each tortilla; roll up.
Place in a large (13x9x2-inch) baking dish.
Pour tomato mixture over all.
Pour enchilada sauce evenly over top.
Cover with foil and bake at 350ºF for 15 minutes.
Uncover and bake for another 15 minutes.
Sprinkle with remaining shredded cheese; return to oven until cheese melts, 2 or 3 minutes.