Preheat grill to medium-high heat. Combine beef, salt, pepper, garlic powder, and soy sauce.
Shape mixture into 12 thin patties. Combine parsley, mushrooms, onion, and bell pepper;
divide mixture among 6 patties. Top each with another patty; seal edges to enclose mushroom mixture.
Grill, covered, 5 minutes per side or until meat is no longer pink.
Top with cheese; grill 1 to 2 minutes longer until cheese melts.
Melt butter and oil in a large skillet over medium-high heat.
Add onion to skillet; sauté 2 minutes. Add mushrooms; sauté 5 minutes.
Stir in spinach, and cook 2 minutes or until wilted; sprinkle with salt and pepper.
Serve and Enjoy