Ingredients

3/4 cup dried brown lentils, rinsed and picked over

2 1/2 teaspoons table salt

3/4 cup bulgur wheat

2 tablespoons vegetable oil

2 medium onions, chopped fine (2 cups)

1 large celery rib, chopped fine (about 1/2 cup)

1 small leek, white and light green parts only, chopped fine (about 1/2 cup)

2 medium garlic cloves, minced or pressed through garlic press (2 teaspoons)

1 pound cremini or white mushrooms, cleaned and sliced about 1/4 inch thick (about 6 1/2 cups)

1 cup raw unsalted cashews

1/3 cup mayonnaise

2 cups panko (Japanese bread crumbs)

Ground black pepper

12 burger buns for serving

Preparation

Bring 3 cups water, lentils, and 1 tsp salt to boil in medium saucepan over high heat; reduce heat and simmer, uncovered, stirring occasionally, until lentils are just beginning to fall apart, about 25 minutes. Drain and dry. Cool lentils to room temperature.

While lentils simmer, bring 2 cups water and 1/2 tsp salt to boil in small saucepan. Stir bulgur wheat into boiling water and cover; let stand off heat until water is absorbed, 15-20 minutes. Drain in fine-mesh strainer; press out excess moisture. Transfer bulgur to medium bowl and set aside.

Heat 1 tbsp oil in 12-inch nonstick skillet over medium-high heat. Add onions, celery, leek, and garlic; cook, stirring occasionally, until vegetables begin to brown, about 10 minutes. Spread vegetable mixture on second baking sheet to cool; set aside. Add remaining 1 tbsp oil to skillet; heat then add mushrooms and cook, stirring occasionally, until golden brown, about 12 minutes. Spread mushrooms on baking sheet with vegetable mixture; cool to room temperature.

Process cashews in food processor until finely chopped; stir into bulgur along with cooled lentils, vegetable-mushroom mixture, and mayonnaise. Transfer half of mixture to food processor and pulse until coarsely chopped; mixture should be cohesive but roughly textured. Transfer mixture to large bowl; repeat with remaining mixture. Stir in panko, 1 teaspoon salt, and pepper to taste.

Line baking sheet with paper towels. Divide mixture into 12 portions, about 1/2 cup each; set patties on baking sheet. (Patties can be covered with plastic wrap and refrigerated up to 3 days.)

Grill burgers, without moving them, until well browned, about 5 minutes; flip burgers and continue cooking until well browned on second side, about 5 minutes.