Sweet Potato Tofu Burger

Name: Sweet Potato Tofu Burger
Ingredients: 1 medium sweet potato, peeled and cut into 1 1/2-inch cubes; 1 small onion, finely chopped; 1 clove garlic, minced; 1 1/2 teaspoons best-quality curry powder; 1/4 teaspoon ground cumin; 2 tablespoons tomato paste; 3 tablespoons potato starch; 1 pound firm tofu; 1/2 cup brown rice, cooked; 2 tablespoons minced chives; 3 tablespoons roughly chopped cilantro; 3/4 teaspoon salt; 1/8 teaspoon freshly ground pepper; 4 low-fat whole-wheat buns; Olive-oil cooking spray