Stashcook | Vegetarian Burger

Ingredients

• 1/2 cup mayonnaise
• 1 Tbsp. adobo sauce from a can of chipotle chiles in adobo
• 1 Tbsp. olive oil
• 1 medium yellow onion, finely chopped
• 1 1/2 tsp. kosher salt, divided, plus more to taste
• 3 garlic cloves, minced
• 1 tsp. smoked paprika
• 1/2 tsp. chili powder
• 1 x 8 oz. block cheddar cheese, shredded
• 1 x (15 oz.) can black beans, drained and rinsed
• 1 large egg, beaten
• 1/2 cup panko breadcrumbs
• 4 whole wheat buns, split
• Unsalted butter, for buns
• Shredded lettuce, sliced red onion, and sliced tomato (for serving)