Preheat the oven to 375 degrees F. (Skip this step if you plan to pan fry)
In a small pan on the stove, sauté the mushrooms over medium heat until soft, about 7 to 8 minutes.
To the bowl of a food processor, add the mushrooms along with the lentils, brown rice, green onions, garlic, mayo, and soy sauce and pulse until well combined, but not puréed.
Transfer the mixture into a large bowl and add the breadcrumbs. The mixture should form easily into patties. If it's too wet, add another 1 to 2 tablespoons of breadcrumbs. If it's too dry, add another splash of soy sauce or even water.
Form the mixture into 6 patties. You can cook them right away or place the patties in the fridge in a single layer for 30 minutes to firm up even more.
Bake the patties in the oven for 25 to 30 minutes, flipping them over half way through. Alternately, you can pan fry in a tablespoon of oil for about 5 minutes each side on medium heat.
Lay your lettuce leaves flat, top each one with a burger, raw shredded veggies, if using, fresh cilantro, if using, and a drizzle of the Sesame Dressing. Wrap them up and enjoy!