Directions

1. Coat grill rack with nonstick cooking spray. Preheat grill to medium (300°F to 350°F). Cut onion into quarters, leaving the stem end intact. Grill onion 10 to 15 minutes per side or until softened, turning once. Remove from grill and let cool. Thinly slice; discard stem end.
2. In a small bowl combine sliced onion, vinegar, mustard and 1/4 teaspoon of the thyme. Set aside.
3. In a medium bowl mix ground beef with remaining 3/4 teaspoon thyme, and soup mix. Shape into 4 (3/4-inch thick) patties.
4. Place patties on grill. Grill, covered, 8 minutes. Turn, top with cheese, and grill 7 minutes more or until instant-read thermometer registers 160°F. Place rolls, cut side down, on grill to toast. Place burgers in rolls, top with onion mixture, and serve.