01 - Preheat oven to 400°F. Grease a 9x13-inch baking dish.
02 - Season chicken breasts with salt and pepper on both sides.
03 - Heat olive oil in a large skillet over medium-high heat. Sear chicken breasts for 2–3 minutes per side until golden. Remove from skillet and set aside.
04 - In the same skillet, add mushrooms. Sauté for 3–4 minutes until softened. Add garlic and cook for 30 seconds until fragrant.
05 - Add spinach and cook until just wilted, about 1 minute. 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 on 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 rest for 5 minutes before serving.