Smoky Veggie Burgers

Name: Smoky Veggie Burgers
Ingredients: 2 tablespoons vegetable oil, plus more for the grill; 1/3 cup finely chopped walnuts; 1 shallot, finely chopped; 2 cloves garlic, minced; 8 ounces cremini mushrooms, finely chopped; Kosher salt and freshly ground pepper; 1 tablespoon Worcestershire sauce; 1 teaspoon smoked paprika; 2 teaspoons Dijon mustard; 1 large sweet potato; 1 1/4 cups cooked quinoa, cooled; 1/2 cup breadcrumbs; 4 hamburger buns, split; Sliced red onion and sprouts, for serving