Put sweet potatoes in a large saucepan and cover with water.
Bring water to a boil; reduce heat and simmer for about 15 minutes, until sweet potatoes are tender. Drain and set aside.
Heat a large skillet over medium heat; coat with cooking spray.
Add chopped onions and garlic and sauté for about 5 minutes, until tender.
Put the sweet potato, onions and garlic, oats, and seasonings into a food processor. Process until smooth.
Divide the mixture into six equal parts, shaping each one into a 1/2-inch thick patty.
Heat oil in a pan over medium heat. Add patties to the pan, as many as will fit, and cook for about 4 to 5 minutes, or until brown. Turn the patties over and cook for another 3 minutes. Set cooked patties aside while you cook the rest.
Serve on whole grain buns. Garnish with lettuce, tomato, and condiments of your choice.
