Heat a large ovenproof skillet over medium-high heat. Add oil; swirl to coat. Sprinkle chicken with pepper and salt. Add chicken to pan; sauté 2 minutes on each side or until browned. Remove chicken from pan.
Add broth, syrup, thyme, and garlic to pan; bring to a boil, scraping pan to loosen browned bits.
Cook 2 minutes, stirring frequently. Add vinegar and mustard; cook for 1 minute, stirring constantly. Return chicken to pan, and spoon mustard mixture over chicken.
Bake at 400° for 10 minutes or until the chicken is done. Remove chicken from pan; let stand 5 minutes.
Place pan over medium heat; cook mustard mixture 2 minutes or until liquid is syrupy, stirring frequently. Serve with chicken.