01 - Preheat oven to 400°F. Grease a 9x13-inch baking dish lightly with oil or cooking spray.
02 - Pat chicken breasts dry with paper towels. Season both sides generously with salt and black pepper.
03 - Heat olive oil in a large skillet over medium-high heat until shimmering. Add chicken breasts and sear for 2-3 minutes per side until golden brown. Transfer to a plate and set aside.
04 - In the same skillet, add sliced mushrooms. Sauté for 3-4 minutes until softened and lightly browned, stirring occasionally.
05 - Add minced garlic to the mushrooms and cook for 30 seconds until fragrant. Add fresh spinach and cook for 1 minute until just wilted. Remove from heat.
06 - Arrange seared chicken breasts in the prepared baking dish. Top evenly with the mushroom-spinach mixture.
07 - Pour heavy cream evenly over the chicken and vegetables. Sprinkle shredded mozzarella cheese across the top.
08 - Bake uncovered for 25-30 minutes until chicken is cooked through (internal temperature reaches 165°F) and cheese is golden and bubbly.
09 - Let the dish rest for 5 minutes before serving to allow juices to redistribute.