Pre-heat oven to 400 degrees. Wash chicken and remove excess fat.
Stir mustard, 1 tsp. lemon zest, oregano, thyme, salt, and 1 tsp. olive oil in a small bowl.
Stir remaining lemon zest, lemon juice and chicken stock in another bowl.
Use your fingers or a brush to coat the chicken on both sides with the rub.
Heat remaining Tblsp. of oil in a large, oven safe skillet or frying pan. Add smashed garlic, cook for 1 minute, or until you can smell toasted garlic and the garlic has browned around the edges. Remove the garlic, but leave the oil.
Now, add chicken skin side down into hot oil and cook 2-3 minutes or until skin has turned golden brown.
Flip chicken, then add lemon juice mixture. Slide pan into pre-heated oven and bake 25 to 35 minutes, or until a meat thermometer inserted into thickest part of chicken reads 175 degrees F.
Remove pan from oven and transfer chicken to a warm plate and cover with aluminum foil. Place pan with liquid over medium heat, and bring to a simmer.
Mix butter and flour together to make a paste. Whisk the paste into the liquid in the pan. The sauce should thicken slightly and become glossy.
Place chicken back in pan, or on a platter, and serve with sauce. Goes well with rice and vegetables, mashed potatoes, or even pasta. Enjoy!