Rinse the dry lentils. Place lentils in a small to medium saucepan and cover with 2 cups of water; add ½ teaspoon salt. Bring to a boil over medium heat. Once boiling, reduce heat to low to keep simmering and cover loosely. Cook lentils for around 20 minutes, until lentils are soft but not falling apart. If they are not done at this point, check every 5 minutes until done. Strain if needed and let cool on a baking sheet.
To make flax egg, combine ground flaxseed meal with ⅓ cup warm water. Stir and let sit for 10 minutes.
Chop onion and garlic in a food processor.
Place lentils, black beans, rolled oats, psyllium husk, chili powder, smoked paprika, black pepper, and remaining sea salt in food processor bowl. Pulse several times until it comes together.
Add oat flour, flaxseed mixture, carrot, sunflower seeds, and parsley. Pulse a few times until just combined. Turn into a bowl and combine thoroughly with spatula. The mixture should hold together easily when you pinch it with your fingers. Taste and adjust seasoning as needed.
Form 8 patties with your hands. Scoop with ½-cup measuring cup; each patty is approximately 3.5 oz.
Heat a non-stick skillet over medium heat. Add a teaspoon of grapeseed oil if using. Cook the burgers for 3 to 5 minutes on each side until golden, adjusting heat as necessary.
Serve immediately with buns, lettuce, sliced tomato, and your favorite toppings.
Notes
Note: Drain and rinse canned lentils and canned black beans. If using precooked lentils, use 1 ⅔ cup.Burgers can be refrigerated for 3 days or frozen up to 3 months, cooked or uncooked. Reheating method is the same as the cooking method on the stovetop.You can cook these patties on a stovetop grill pan, and follow the same instructions. If you want to cook these lentil black bean burgers on a grill outside, it should be fine since these burgers hold together well.