Pre-heat oven to 350 degrees.
Heat a large saute pan over medium heat and add olive oil. Add onion and saute for a 3-4 minutes and then add garlic and saute for another minute until garlic is fragrant and onions are translucent.
Add spinach and cook until spinach is wilted, stirring frequently. Approximately another 2 minutes. Remove from pan and set aside to cool.
Add ricotta cheese, Parmesan cheese, parsley, salt and pepper to a medium sized bowl. When spinach is cool, add to bowl and mix well.
Lay butterflied chickens out on surface and season each side with salt and pepper. Fill each half with cheese mixture. Gently fold other half of the chicken breast over the cheese mixture and gently press to close.
Melt butter on low medium in the same saute pan used for spinach.
Turn heat up to medium high and with tongs holding the chicken breasts together so the stuffing doesn't spill out, gently lift the stuffed chicken and place into hot pan. Sear on one side for 3 minutes, then gently flip with tongs to sear the other side.
Once seared, place pan into the oven and finish cooking for 35-40 minutes.
While chicken finishes, in a medium sauce pan over medium low heat, add butter and flour for gravy. Whisk constantly to form a roux. Slowly add the stock will continuously whisking.
Once all of the stock is added, add salt and continue cooking to reduce to desired thickness.
When chicken is finished cooking, remove from oven, plate and serve with hot gravy.
Serve with your favorite mashed potatoes.