The Ultimate Veggie Burger for Grilling

Name: The Ultimate Veggie Burger for Grilling
Ingredients: 3/4 cup old-fashioned rolled oats; 1/2 cup walnuts, toasted; 3 medium scallions, coarsely chopped (about 1/4 cup); 2 (15-ounce) cans black beans, drained and rinsed (about 3 1/3 cups); 1/2 cup shredded carrot (from 1 medium, unpeeled carrot); 1/4 cup white miso paste; 1 tablespoon chili powder; 3 tablespoons olive or canola oil; For serving: 6 split hamburger buns, ketchup or mustard, lettuce, sliced tomato, thinly sliced red onion