1 small onion, quartered
1 (14-ounce) can chickpeas, drained and rinsed
1 cup chopped walnuts
1 cup panko breadcrumbs
1 tablespoon ground flaxseed
2 garlic cloves, minced
2 tablespoons vegan Worchestershire sauce
1 tablespoon red wine vinegar
1 tablespoon soy sauce
1 teaspoon paprika
1/4 teaspoon black pepper
Olive oil, for grilling
4 tablespoons horseradish mustard
1 tablespoon maple syrup
4-6 burger buns
4-6 lettuce leaves
1 large tomato, sliced
Onion slices