Preheat grill to MEDIUM.
Rub garlic into chicken then season evenly with salt and pepper. Lightly oil the grill grate; grill chicken over indirect heat for 6 to 8 minutes per side or until juices run clear.
Watch carefully to prevent burning! Meanwhile, heat 1 tablespoon of olive oil in a large, deep skillet over medium heat. Add green onions and cook and stir for 2 minutes or until fragrant.
Add mushrooms and cook and stir for 5 to 7 minutes or until just tender. Add broth to the pan. Bring mixture to a boil then add spinach and cook for 2 to 3 minutes or just until spinach has wilted.
Top each chicken breast half with 1 slice of cheese and a portion of the spinach mixture. Top with chopped pecans if desired and enjoy!