Preheat oven to 350 degrees and lightly grease a baking dish that's big enough to hold 4 chicken breasts.
Make mushrooms. Heat butter and oil in a large pan over medium-high heat. Add mushooms and cook until water has evaporated and they are golden brown.
Add garlic powder and Worcestershire sauce. Season to taste with salt and pepper. Remove mushrooms from pan and set aside.
Sprinkle seasoned salt, pepper, and garlic powder on both sides of chicken breasts and place in prepared baking dish. Bake for 15 minutes.
While chicken bakes, make creamed spinach. Heat butter and oil over medium heat in the same pan you cooked the mushrooms in. Add onion and cook until soft.
Add spinach a few handfuls at a time, adding more as it wilts down. Once wilted, add seasoned salt, cream cheese, Parmesan cheese, and red pepper flakes. Turn heat to low and stir until cheese is melted. Remove from heat.
Once chicken has baked for 15 minutes, remove from oven and flip chicken over. Top with spinach, mushrooms and mozzarella slices.
Place chicken back in oven and bake for 16 to 18 minutes, or until chicken is cooked through.