Preheat oven to 400°F. Put tortillas on baking-sheet & spray on every side with non-stick cooking-spray.
Then bake the tortillas for 4minutes on each side, or till edges are slightly-curled. Remove from oven and put aside.
In a small-bowl add the refried beans, cumin powder, lime juice and chili powder. Mix all ingredients together and microwave for a few minutes, or till beans warm.
Cut avocado in half, remove pit then slice into thin strips and scoop the green-flesh from the shell using a spoon.
Assemble tostadas by topping each toasted tortilla using ¼ cup refried-bean mix, ¼ cup pico de gallo, 4 avocado slices, a tbsp black-olives and 2-tbsp crumbled queso fresco.
Serve as is or squeeze a little lime-juice on the top of every tostada prior to serving.