Heat 2 tablespoons of extra-virgin olive oil in a large skillet over medium heat. Add 1 finely chopped shallot and sauté for about 1 minute until softened. Then, incorporate 16 ounces of sliced shiitake and portobello mushrooms. Continue to sauté for 6 to 9 minutes until the mushrooms are browned and their moisture has evaporated.

Stir in 2 tablespoons of tamari, 2 tablespoons of balsamic vinegar, and 1 tablespoon of mirin to the sautéed mixture. Next, add 2 minced garlic cloves, ½ teaspoon of smoked paprika, and 2 teaspoons of sriracha. Mix well and let the mixture cool slightly.

Transfer the cooled mushroom mixture to a food processor. Add ½ cup of chopped walnuts, ¼ cup of ground flaxseed, and 2 cups of cooked short-grain brown rice. Pulse until combined yet retains some texture—for about 10 seconds.

Take the blended mixture out of the food processor and place it in a mixing bowl. Fold in ½ cup of panko bread crumbs until evenly distributed. Form into 8 equal-sized patties, and chill in the refrigerator for 1 hour.

Preheat your grill to medium-high heat, around 375°F to 400°F. Lightly brush the patties with extra-virgin olive oil.

Place the chilled patties on the preheated grill. Cook each side for about 7 minutes, or until nicely charred and heated through.

For an alternative, cook patties in a non-stick skillet over medium heat for about 5 to 6 minutes on each side until golden and charred.

Assemble by placing each patty on a hamburger bun and topping with your favorite fixings.