Mash the sweet potato and garbanzo beans in a large bowl. Fold in the remaining ingredients until well combined. Then form the sweet potato mixture into 6 patties.
Melt one teaspoon of butter substitute in a grill pan over medium heat. Place 3 patties on the grill pan, cooking each side for 5 minutes or until crusted. Remove from heat and repeat with the remaining 3 patties.
Use the remaining teaspoon of butter substitute to coat each side of the 6 buns. Place them on the hot grill pan for 15-20 seconds, then turn over and toast the opposite side.
Serve each sweet potato burger with avocado slices.
Notes
If making 4 burgers, cook each side for an additional 1-2 minutes.