- Preheat the oven to 375°F . Line a baking sheet with parchment paper or a silicone baking mat.
- Heat the oil in a large frying pan over medium heat. Add the onion, garlic, and mushrooms and sauté until the mushrooms are tender and the onions are translucent, 4 to 5 minutes. Remove from the heat and transfer to a food processor.
- Add 1 cup of the lentils, the liquid aminos, nutritional yeast, Worcestershire sauce (if using), cumin, parsley, paprika, salt, and pepper. Pulse until fully combined and all pieces are similar in size.
- Transfer to a large bowl. Add the remaining lentils, the oats, quinoa flour, almond flour, and flax meal and mix until a thick dough forms.
- If it’s too liquidy, add more oats. If it’s too dry, add water by the tablespoon until it’s no longer crumbly. It should hold together without crumbling when squeezed.
- Use your hands to form the mixture into 8 patties and place them on the baking sheet. Bake for 20 minutes, flipping once halfway through to ensure even cooking. Drizzle cheese sauce over the tops and bake for another 5 minutes.
- To assemble, spread ketchup, mustard, mayonnaise, and/or relish on the top and bottom halves of the buns. Place some lettuce on the bottom bun and stack two patties on top.
- Top the patties with tomato, red onion, and/or pickles, as desired. Serve immediately. Leftover burgers will keep in an airtight container in the fridge for 4 to 5 days.