Heat the oil in a pan and gently fry the onion and garlic for 4-5 minutes, or until softened. Increase the heat and fry the mushrooms for 3 minutes. Stir in the curry powder and cook for another minute. Set aside and allow to cool.Place the sweet potato, rice, breadcrumbs, coriander and egg into a mixing bowl. Season with salt and pepper and mix well. Add the mushroom mixture and mix together. Using lightly floured hands, shape spoonfuls of the mixture into rissoles or patty shapes. Coat both sides of the rissoles in gluten-free flour or polenta. Lightly brush both sides of the rissoles with olive oil and lightly fry, or cook under a grill for 3-4 minutes per side, or until golden. Pat dry on paper towel. Serve in lettuce cups, with grated carrot, sliced red onion and some guacamole.