In a nonstick skillet over medium-high heat, sauté onions and mushrooms in olive oil for 3-5 minutes, until the extra moisture shed from the mushrooms cooks off.
Add in garlic and sauté for another minute.
Add in tomato paste and stir to coat ingredients. Cook for another 1-2 minutes, stirring often, until the tomato paste darkens from a vibrant red color to a deep rust color. Remove from heat.
To a food processor, add cooked lentils, mushroom mixture, sunflower seeds, soy sauce, and smoked paprika. Process until mixture is well-combined but still has a little bit of texture. Scrape down the bowl of the food processor as needed to ensure the texture is consistent.
Add breadcrumbs and stir to combine. The mixture should be moist enough that it sticks together and doesn't crumble. However, it shouldn't be so wet that it sticks to your hands. If the mixture is still a little on the wet side, add in additional breadcrumbs a few tablespoons at a time and mix well between additions.
Divide mixture and shape into patties. Typically I shape mine into 4 or 5 medium-sized burgers, but you can make them larger or smaller as you prefer. You can even shape them into meatballs.
Preheat about 1 tablespoon olive oil in a nonstick skillet or cast iron over medium-high heat.
Pan-fry shaped patties 2-3 minutes per side, or until deep golden brown. Enjoy.