Using a food processor, finely chop the onion, carrots, garlic, walnuts and sunflower seeds then transfer to a large bowl. I process each ingredient individually to achieve the best texture.
Next add half of the cooked lentils to the food processor and pulse until they appear slightly mashed, then transfer them to the bowl along with the remaining lentils.
Once you have all of the vegetables, lentils, nuts and seeds in the bowl, add the breadcrumbs, herbs, and salt.
In a small bowl, combine the beaten egg with the tomato paste and the Worcestershire. Pour the egg mixture into the bowl with vegetables and lentils and stir everything together. Sprinkle in the flour a little at a time as you continue to stir. If the mixture seems too wet, add more flour as needed. If you have time, refrigerating the mixture for about 30 minutes also helps dry out some of the moisture.
Form eight individual patties with your hands, making sure to keep them somewhat flat with rounded edges. They will hold together better if they aren’t too big or thick. At this point you can refrigerate them until you are ready to cook (for up to 2-3 days) or cook them right away.
When you’re ready to cook them, start by warming the olive oil over medium-heat in a skillet for at least five minutes. Once the skillet is thoroughly heated, cook the burgers on each side for about 5-6 minutes. I like the push the edges of the burger to the side of the pan as I cook them to make sure they are cooked on the sides as well. Serve on a warm bun with desired toppings and dig in!