Goat Cheese–Stuffed Lamb Burgers with Caramelized Red Onions

Name: Goat Cheese–Stuffed Lamb Burgers with Caramelized Red Onions
Ingredients: 1 tablespoon butter; 1 large red onion, thinly sliced (about 2 cups); 1/4 teaspoon kosher salt; 1/4 cup dark beer; 1 1/2 pounds ground lamb; 1 garlic clove, minced; 1/2 teaspoon smoked paprika; 1/4 teaspoon cayenne pepper; 1 tablespoon chopped fresh mint; 1/3 cup goat cheese; Kosher salt and freshly cracked black pepper; 1 tablespoon olive oil; 4 burger buns; 4 tablespoons Spicy Herb Mayo; 4 slices cooked bacon; 1 cup baby arugula