Place the Lentils (3/4 cup) and Water (1 1/2 cup) in a small saucepan and bring to a boil. Lower the heat and simmer, partially covered, for about 20-25 minutes or until the lentils are soft and the water is absorbed.
Transfer to a medium sized bowl with the Apple Cider Vinegar (2 teaspoon), and mash using the back of a large spoon.
While the lentils are cooking, heat Olive Oil (2 tablespoon) over medium-high heat in a large sauté pan. Cook the Yellow Onion (1) until translucent, about 3 minutes.
Add the Button Mushroom (10) and continue to cook until soft, another 3 minutes.
Add the Garlic (2 clove) and cook until fragrant, about 45 seconds. Add the Walnut (1/2 cup) and Fresh Parsley (2 tablespoon) and mix until combined.
Season with the Dry Mustard (1 teaspoon) and a squeeze of Lemon (to taste). Start with 1/2 teaspoon of salt and 1/4 teaspoon of pepper, then add more Salt and Pepper (to taste) or other seasonings until desired taste achieved.
Add the cooked vegetables and Breadcrumbs (1/2 cup) to the lentils and mix well. Chill for 1 hour before forming patties.
Form 4-inch diameter burgers. The mix will yield 4-6 burgers, depending on how thick you make your burgers.
When ready to cook, preheat the broiler to high.
Transfer burgers to a sheet pan and broil 5-8 minutes until heated through and crispy. Keep an eye out, every oven is different.
Serve on Hamburger Bun (4), sliced Tomato (to taste), Vegan Aioli (to taste), Pickled Red Onions (to taste), Alfalfa Sprouts (to taste), or any desired toppings. Enjoy!