Heat oven to 425°F. Spray 18x13x1-inch pan with cooking spray. In large bowl, mix 2 tablespoons of the melted butter, 1 tablespoon of the soy sauce and the pepper flakes. Add sweet potatoes and bell pepper; toss to coat. Transfer to pan in single layer. Do not clean bowl. Mix remaining 2 tablespoons melted butter and 1 tablespoon soy sauce in bowl; add chicken, and toss to coat. Add chicken to pan with vegetables. Roast 20 minutes.