Preheat oven to 400 degrees. Line a baking sheet with foil and lightly spray with cooking spray.

In a small bowl whisk together mustard, honey, oil, salt, pepper. Slice Brussel sprouts in half, peel sweet potato and cut into cubes, chop onion. Cut chicken into large pieces. Add veggies and chicken to a large bowl with a top. Pour in the mustard mixture, seal off container and shake to coat.

Place veggies and chicken onto baking sheet. Bake for 30 minutes, checking to be sure the chicken is no longer pink in the center and veggies have become tender.

Serve hot with plum slices on the side.