1. Place chopped mushroom, black beans, almond butter, 1 tablespoon mayonnaise, pepper, 1/2 teaspoon garlic powder, and salt in a food processor. Pulse, stopping once or twice to scrape down the sides, until a coarse mixture forms that holds together when pressed. Transfer to a bowl and add quinoa and oats; stir well to combine. Refrigerate for 1 hour.
2. While mushroom mixture chills, whisk ketchup, mustard, and the remaining 2 tbsp mayonnaise and 1/4 teaspoon garlic powder in a small bowl until smooth. Set aside.
3. Shape the chilled mushroom mixture into four patties.
4. Heat oil in a large grill pan or nonstick skillet over medium-high heat. Add the patties and cook until golden and beginning to crisp, 4 to 5 minutes. Carefully flip and cook until golden brown, 2 to 4 minutes more.
5. Serve the burgers on buns with the special sauce and add your favorite toppings, such as lettuce, spinach, pickles, tomatoes, jalapeños, and/or red or sweet onions.
Calories: 494; Total Fat: 15.8g; Saturated Fat: 2.1g; Cholesterol: 3mg; Sodium: 559mg; Total Carbohydrate: 72.6g; Dietary Fiber: 13.3g; Total Sugars: 6.6g; Protein: 19.8g; Calcium: 121mg; Iron: 6mg; Potassium: 1117mg