Clean and chop mushrooms to a small size. Heat olive oil in a large pot over medium heat. Add the onion and cook over medium heat for 10 minutes. Add the mushrooms and cook for another 10 minutes until the mushrooms have reduced and the onion is translucent. Add the lentils and water, bring to a boil and reduce heat to simmer for 30 minutes. Remove from heat and let cool for 5 minutes. Pour the mixture into a large mixing bowl. Add a dash of kosher salt, paprika, hot red pepper and cumin. Add the egg and bread crumbs, and combine using a potato masher. Mash the lentils until about half are completely mashed and half are still intact. Slowly add the flour until the lentil mixture is not too wet. Add the walnuts and sundried tomatoes and stir to combine.

Using your hands, form a small portion of the mixture into a patty. Repeat until you have used all of the mixture. Heat a skillet to medium high coat with cooking spray. Working in batches, add a few burgers and flip after 4 minutes. When other side has crisped, remove and repeat. Serve with slices of avocado, tomato, and/or hummus.