Make tostada shells: Pour 1/4 inch of oil into a small skillet. Heat oil to 350°F.
Place one tortilla in oil and fry until the tortilla starts to crisp and the bottom side of the tortilla begins to brown. Turn the tortilla over and fry the other side. Flip again and fry until golden brown. Remove from pan and place on paper towels to drain. Repeat with remaining tortillas.
Dress lettuce (optional): Toss lettuce with two tablespoons of dressing.
Assemble tostadas: Place one tostada shell on a plate.
Spread a thin layer of beans on the tostada shell.