1Heat oven to 375°F. Fold wings of chicken under back. Tie or skewer drumsticks together. Place chicken, breast side up, on rack in shallow roasting pan. Arrange squash and onions around chicken.
2In small bowl, mix remaining ingredients; brush on chicken and vegetables just until evenly coated. Reserve remaining butter mixture. Insert meat thermometer in chicken so tip is in thickest part of inside thigh muscle and does not touch bone.
3Roast uncovered 1 hour. Brush remaining butter mixture on chicken and vegetables. Cover loosely with foil to prevent overbrowning. Bake 45 to 55 minutes longer or until thermometer reads 180°F, juice of chicken is no longer pink when center of thigh is cut and squash is tender.