Cook the lentils: In a medium pot, add the lentils and water. Bring to a boil over high heat, then reduce heat and simmer, uncovered, for 15-18 minutes, until the lentils are tender but not mushy. Drain in a fine mesh colander, then spread them in an even layer on a clean dish towel or paper towels to absorb excess water. We don't want mushy burgers!
Add the cooked lentil to a food processor and pulse several times, until there are just a few whole lentils left. Transfer the mashed lentils to a large bowl.
To the large bowl with the lentils, add the chopped red onion, minced garlic, chopped walnuts, ground flaxseeds, ketchup, Worcestershire sauce, ground cumin, smoked paprika, parsley or cilantro, salt, and breadcrumbs. Mix with a large spoon until well combined. Alternatively, mash the lentils in a bowl and then add the rest of the ingredients and mix with a spoon.
Using about 1/2-3/4 cup per burger, shape into burger shapes about 1-1 1/2 inches thick. I got 4 thick burgers from the recipe.
To Pan Fry: Add 2-3 tablespoons olive oil to a non-stick or cast iron pan over medium heat. Add 3-4 burgers at a time and cook on one side until crispy and golden, about 4 minutes. Flip and cook for 3-4 minutes more, then transfer to a plate.
To Bake: Preheat the oven to 350 degrees F and line a baking sheet with parchment paper. Place the burger patties on the pan and bake for 15 minutes, then flip carefully and bake for 15 more minutes.
Serve on buns with toppings of choice and enjoy!