1 can (15 1/2 ounces) black beans, or red kidney beans, rinsed and drained
2 teaspoons olive oil
1 teaspoon ground cumin, or more to taste
1/4 teaspoon chili powder
1/2 teaspoon salt
6 flour tortillas, (10 inches in diameter)
3 plum tomatoes, seeded and cut into 1/4-inch dice (about 1/2 cup)
1 cup shredded cheddar cheese
6 large green-leaf lettuce leaves
1 avocado, cut into 1/4-inch dice, for serving (optional)
1 mango, cut into 1/4-inch dice, for serving (optional)