Spray the pan with low-calorie cooking spray and place over a medium to high heat.
When the pan is hot, add the chicken breasts and cook for 1-2 minutes each side to seal and colour. When golden, remove from the pan and place to one side.
Reduce the heat to medium and add the onions. Sauté for 5 minutes until soft, then add the garlic and cook for a further minute.
Add the stock and cream cheese and stir until thoroughly mixed.
Return the chicken to the pan, bring to a boil and cook at a fast simmer for 20 minutes, flipping the chicken breasts over halfway through to ensure even cooking.
After 20 minutes, the sauce should be the consistency of single cream. If it is too watery, increase the heat and cook until the desired consistency is reached.
Stir in the parmesan and black pepper.
Add the spinach to the pan and stir for a minute until it has wilted.
Serve!