Grilled Tuscan Style Burgers

Instructions

1. Prepare a grill or heat grill pan to medium high heat.
2. Slice the red onion into 1/3 inch rings. Place them on the hot grill and season them with ½ teaspoon salt. Cook the onions, flipping halfway through, until lightly charred and softened, 6 to 8 minutes. Remove to a plate.
3. In a medium bowl combine the ground beef with the mustard and rosemary. Mix gently but thoroughly to combine. Divide into 4 equal pieces and form into patties. Season evenly on both sides with the remaining 1 1/2 teaspoons of salt and the pepper. Place the burgers on the preheated grill and cook to desired doneness, 3 to 4 minutes per side for medium. Top the burgers with 1/4 cup of cheese for the last 2 minutes of cooking.
4. Divide the arugula on the bottom halves of each bun. Top with a burger and divide the onions on top of the burgers. Garnish with condiments of your choice and serve.