Five-Ingredient Veggie Burger

Name: Five-Ingredient Veggie Burger
Prep time: 35 min
Cook time: 20 min
Total time: 55 min
Cuisine: American
Ingredients: 2 cups no-salt-added canned black beans, drained and liquid reserved; 1 medium onion, quartered; ½ cup quick-cooking rolled oats (see gluten-free tip, recipe intro); 1 Tbsp. lime juice; 2 tsp. chili powder (see gluten-free tip, recipe intro); Sea salt and freshly ground black pepper, to taste; Avocado oil cooking spray (optional, learn more); 4 100% whole grain hamburger buns, split and toasted (see gluten-free tip, recipe intro); 4 leaves leaf lettuce; 1 tomato, sliced; 2 red onion slices, separated; Condiments of your choosing (see headnote)