Traditional refried beans are prepared very much like their name suggests. Cooked beans are mashed and fried, often in lard. Check your grocery aisle for equally tasty refried beans that are fried in vegetable oil if you're concerned about saturated fats.
If you like your tacos "loaded," then load these up, too! Chopped or sliced jalapeños, sliced ripe or green olives, chopped tomato or chopped bell pepper will bulk them up in colorful, delicious style!