Best Veggie Burger Ever

Ingredients

• ***For the burger:***
• 3 tablespoons olive oil, divided, plus more, to taste
• 1 medium yellow onion, minced
• 2 large cloves garlic, minced
• 1 (15-ounce) can garbanzo beans, drained and rinsed
• 2 cups white rice, cooked
• 1 cup walnuts, finely crushed after measuring
• 3/4 cup whole-wheat flour
• 1 tablespoon cumin
• 1 1/2 teaspoons garlic powder
• 1 1/2 teaspoons onion powder
• 1 1/2 teaspoons kosher salt
• 1 teaspoon black pepper
• 1 egg white
• barbecue sauce, to taste
• ***Optional, for serving:***
• 6 hamburger buns
• guacamole, to taste
• tomato, sliced
• lettuce leaves, to taste