Preheat the oven to 300°. Place the shells in a tortilla warmer or a covered casserole dish. Heat until warm.
Heat the oil in a large skillet and sauté the onions for 1 to 2 minutes. Add the rice and beans and the refried pinto beans. Mix thoroughly. Cover and simmer on low until hot, stirring frequently to prevent burning.
When the shells and rice and beans are hot, place a lettuce leaf on each shell. Place an equal amount of rice and beans on each. Place red pepper strips, sliced avocado, and salsa on each. Roll up and place on individual serving plates.
Per serving - 436 calories, 17 g fat (33% calories from fat), 14 g protein, 62 g carbohydrate, 15 g fiber, 0 mg cholesterol, 760 mg sodium