2 pounds ground turkey (preferably 1 pound thigh and 1 pound breast)
1/2 cup dried whole wheat bread crumbs
1/2 cup finely chopped yellow onion
2 tablespoons Worcestershire sauce
1 teaspoon fine sea salt, divided
1 red onion, thickly sliced
1 teaspoon extra-virgin olive oil
6 ounces Gouda cheese, sliced
Prepare a gas or charcoal grill for medium-heat cooking. In a large bowl, combine turkey, bread crumbs, onion, Worcestershire sauce and 1/2 teaspoon salt. Using your hands or a large spoon, gently mix the ingredients together—do not overmix. Divide the mixture into 6 equal portions. Flatten into patties about 5 inches in diameter and no more than 3/4-inch thick (patties will shrink and thicken as they cook).
Skewer the onion slices on metal skewers, putting about 2 slices on each skewer. Brush slices on both sides with olive oil and sprinkle lightly with remaining 1/2 teaspoon salt.
Grill burgers and onion slices until browned on one side, about 4 minutes. Turn burgers and onions and grill on the other side, about 2 minutes. Top burgers evenly with Gouda slices, cover grill, and continue cooking until the onions are browned and the burgers are cooked through and the cheese is melted, about 2 minutes more. Serve burgers topped with onions as they are or in buns with your choice of condiments.