If desired, brown the chicken after coating with mustard mixture. In a 12-inch skillet heat 1 Tbsp. olive oil over medium-high. Add half the chicken. Cook 2 minutes on each side or until browned. Transfer to a shallow baking pan. Repeat with remaining chicken, adding more oil to skillet if needed. Roast as directed in Step 3.
Assemble as directed (don't brown chicken). Chill, covered, up to 8 hours before roasting.