Heat a large skillet over medium-high heat; add 1 tablespoon of the oil.
Brown chicken well on both sides; drain any fat from the pan.
Reduce heat, cover and cook chicken for 30-40 minutes, or until juices run clear or internal temperature reaches 170 degrees F.
Remove cooked chicken and cover to keep warm while you make the sauce.
Drain accumulated stock and reserve 1/2 cup for the sauce. You may store the remainder in a covered container in the fridge for future use. Wipe out the skillet with a paper towel.
Heat the same skillet over medium heat and add the remaining 1 tablespoon of the oil.
Saute the onion and garlic for about 3 minutes or until it becomes fragrant.
Add the undrained tomatoes, the 1/2 cup of stock and the drained spinach. Stir to combine.
Mix the flour with the 3/4 cups of milk, blending so there are no lumps.
Add the milk/flour mixture to the pan, stirring until it becomes thick and begins to bubble.
Add the cream, stirring to blend.
Add the cheese and stir to combine. Add the chicken back to the pan and cook for 5-10 minutes.
Nice with pasta.