Ingredients

• 1 pound cremini mushrooms, halved
• 1 tablespoon extra-virgin olive oil
• 1 large sweet onion, diced
• 1 3/4 cups light beer (drink what's left in the bottle)
• Kosher salt
• 1/3 cup finely chopped walnuts
• 1 small green bell pepper, seeded and diced
• Freshly ground black pepper
• 1/2 teaspoon chipotle chile powder
• 1/4 cup ketchup
• 3 tablespoons tomato paste
• 6 whole grain hamburger buns
• Shredded red cabbage or lettuce, pickled jalapeno and scallions, for serving, optional

Instructions

1. Pulse the mushrooms in batches in a food processor until finely chopped. Set aside.
2. Heat the oil in a large nonstick skillet over medium-high heat. Add the onions, 1 tablespoon beer and 1/4 teaspoon salt and cook, stirring frequently, until the onions are lightly browned, about 5 minutes. Add the walnuts and peppers and cook, stirring occasionally, until the peppers are crisp-tender, about 3 minutes. Add the mushrooms, 3/4 teaspoon black pepper and chipotle powder and cook, stirring frequently, until the mushrooms are just cooked through, about 5 minutes.
3. Add the remaining beer, the ketchup, tomato paste and 1/8 teaspoon salt and cook while stirring until the sauce is the consistency that you like, about 2 minutes.
4. Spoon the mixture onto each bun. Serve with toppings if desired.