Coarsely chop garlic; sprinkle with salt and mash to a paste with the side of the knife. Coarsely chop walnuts in a food processor. Add bread, marjoram, pepper and the garlic paste; process until coarse crumbs form. Add lentils and Worcestershire; process until the mixture just comes together in a mass. Form into four 3-inch patties (about 1/3 cup each).
Heat 2 teaspoons oil in a large nonstick skillet over medium heat. Cook the patties until browned on the bottom, 2 to 4 minutes. Carefully turn over; reduce heat to medium-low. Drizzle the remaining 1 teaspoon oil around the burgers and cook until browned on the other side and heated through, 4 to 6 minutes more. Serve on buns with lettuce, tomato (or red pepper) and onion.