Preheat your oven to 375F and line a baking sheet with parchment.

Heat the onion in a skillet or frying pan over medium heat. Add the carrot, celery, and onion. Cook, stirring often, until the onion is soft and clear and the carrots are tender (about 5 minutes). Add the garlic and cook all ingredients for another minute, stirring as you go. Remove the vegetables from heat.

Place the sunflower seeds into a food processor fitted with the S blade. Grind the sunflower seeds until they're coarsely ground. Add the rice, cooked vegetables, flax, salt, thyme, and rosemary. Add two tablespoons of the water. Pulse about 10 times, or until the mixture is evenly incorporated and clumping together. If the mixture is very dry, add another tablespoon of water and keep pulsing.

Shape the mixture into 6 burgers. Transfer them to a baking sheet. Bake for 30-35 minutes, flipping once halfway through, or until the burgers are browning. Allow to cool slightly before serving.