Preheat your oven to 375°F (190°C).
Lightly grease a baking dish.
Dice the onion and mince the garlic.
In a skillet over medium heat, sauté the garlic and onion until translucent.
Add the chicken breast (cut into bite-sized pieces) to the skillet and lightly brown on all sides.
Once the chicken is lightly browned, remove from heat and mix in the fresh spinach until slightly wilted.
In a bowl, combine the light cream cheese with skim milk; whisk until smooth and creamy.
Season the cream sauce with salt and black pepper.
Pour the sauce over the chicken and spinach mixture, stirring to combine well.
Transfer the mixture to the prepared baking dish and sprinkle the light shredded mozzarella cheese evenly on top.
Bake in the preheated oven for 20-25 minutes until the cheese is melted and bubbly, and the chicken is cooked through.
Serve warm and enjoy your creamy, cheesy chicken and spinach bake.