Rub chicken breasts with the dijon mustard on both sides (TIP: I've added the chicken breasts to a Ziploc bag and then tossed them in the mustard that way, but rubbing them by hand is fine)

Salt and pepper both sides of chicken

Heat butter in dutch oven (or skillet) over Medium to Medium-High heat

Once butter is sizzling a bit, add chicken and sear on Medium-High for 2-3 minutes on each side

Lower heat to Low-Medium, and add lemon juice over the chicken

Cover dutch oven or skillet with lid and cook over Low-Medium heat for 12-15 minutes (depending on the thickness of the chicken breasts and the heat of your stovetop)

Once the chicken breasts have cooked through, take them out and cover with foil for about 5 minutes to rest. Slice chicken breasts diagonally, and drizzle lemon-dijon pan "sauce" over them

Serve with sautéed green beans (TIP: After quickly sautéing, add them to the remaining dijon-lemon sauce in dutch oven, and then season with salt and pepper)