In small skillet cook tortillas, one at a time, in 1/4 inch hot oil for 20 to 40 seconds on each side or till crisp and golden. Drain on paper toweling; keep warm in foil 250 degrees oven. Skin, bone, and cut chicken breasts into very thin strips. In medium skillet quickly cook chicken and onion in butter or margarine till chicken is done adn onion is tender. Add tomato sauce, garlic sats, salt, and cumin. Reduce heat and simmer, covered, for 15 to 20 minutes. To assemble each tostada, place a warm tortilla on serving plate; spoon on chicken mixture; them lettuce, cheese, avocado slices, and olives. Drizzle with bottled hot pepper sauce to taste, if desired. Makes 8 servings.