Shave thorns from cactus pads with a vegetable peeler, leaving green skin; cut cactus pads into thin strips.
Heat oil in a large nonstick skillet over medium-high heat. Add cactus and garlic; sauté 7 minutes or until cactus is tender. Combine cactus mixture, beans, and next 7 ingredients (beans through tomatoes). Arrange 1 1/2 cups lettuce on each of 4 plates; top each serving with 1/2 cup cactus mixture, 1 1/2 tablespoons cheese, and about 2 teaspoons sour cream.