Sprinkle chicken with 1/4 tsp. salt and 1/4 tsp. pepper.
Heat 1 Tbsp. oil in a pan over medium-high heat. Add chicken to pan; cook 3 minutes on each side or until done.
Remove from pan; keep warm.
Add 2 Tbsp. vinegar and syrup to pan; bring to a boil. Cook 1 minute or until reduced. Return chicken to pan; turn to coat with glaze.
Cut Brussels sprouts in half lengthwise; thinly slice crosswise.
Place remaining 1 Tbsp. oil, 1 Tbsp. vinegar, 1/4 tsp. salt, and 1/4 tsp. pepper in a large bowl; stir well with a whisk.
Add Brussels sprouts and apple; toss to combine. Serve slaw with chicken.