Preheat grill or broiler. In a large skillet, heat oil over medium-high heat; saute mushrooms and green onions until tender. Stir in spinach and pecans until spinach is wilted. Remove from heat; keep warm.
Sprinkle chicken with seasoning. Grill, covered, on an oiled grill rack over medium heat or broil 4 in. from heat on a greased broiler pan until a thermometer reads 165°, 4-5 minutes per side. Top with cheese; grill or broil until cheese is melted. To serve, top with mushroom mixture.
Health Tip: This low-carb main dish is also gluten-free.