Heat a skillet over medium heat and add the olive oil. Once the oil is hot, add the diced onion. Sauté for about 5 minutes, until golden-brown.
To a large bowl, add the lentils, brown rice, finely chopped walnuts, cooked onion, Worcestershire sauce, liquid smoke, tomato paste, spices, sugar, and 3/4 cup of the breadcrumbs.
Mash these all together, using your hands if needed, until well-combined. It may be too wet, so continue to add more breadcrumbs until it is workable. You want the mixture to be moist, but not too wet that you cannot form it into patties.
Form the mixture into patties that are about ½ inch thick, using approximately 1/3 cup at a time. Set these on a baking sheet or a plate. Allow them to chill in the fridge for about 30 minutes.
Heat a griddle, cast iron, or non-stick pan over medium heat with some cooking oil, if needed. Once hot, add the patty. Cook for about 2 minutes on each side. Once finished, serve on buns with your favorite toppings!