Put the lean ground beef and chopped onions in skillet over medium heat. Break up meat and fry til brown. Drain grease. Add the tomato sauce, cumin, pepper, salt and chili powder and stir 10 minutes til meat mixture thickens.
Heat oil in skillet. Put tortilla in hot oil and fry on both sides 1 minute til golden and crispy to make tostada. Drain on paper towels. Repeat process with remaining tostadas
Spoon a layer of warm beans, meat mixture, lettuce and salsa on tostadas.top with cheese, sour cream and olive. Serves 4