Preheat the oven to 350°F (175°C). Season the chicken with salt and pepper. Spread one side of every chicken breast half with Dijon. Place two prunes in the center of the mustard coated side and roll the chicken up. Wrap the bacon around each chicken breast and secure with a toothpick.
In a small saucepan, melt the butter and oil. Add the flour and stir for a minute. Add the stock and stir until the gravy has boiled and thickened. Squeeze some lemon juice into it. If needed, add some salt.