Preheat oven to 400 degrees. Cut chicken breasts in half then season both sides with salt and pepper. Spray a 2qt baking dish with nonstick spray then place seasoned chicken breasts in the bottom. Melt butter in a large skillet over medium heat then add shallots. Season with salt and pepper then saute until softened, 2-3 minutes. Add garlic then saute for 30 more seconds. Add cream cheese and Greek yogurt then stir until smooth. Remove skillet from heat then fold in spinach, artichoke hearts, and half the parmesan and mozzarella cheeses. Spoon mixture over chicken then smooth and cover with a piece of foil sprayed with nonstick spray. Bake for 20 minutes then remove foil and top with remaining cheeses. Bake for 10 more minutes or until cheese is golden brown and bubbly then let rest for 10 minutes before serving.