In small bowl, mix mayonnaise and mustard. Spread 1 tablespoon mayonnaise mixture on each of 4 slices of bread. Top each evenly with turkey, cheese and roasted peppers. Cover with remaining slices of bread.
Spray 12-inch skillet with cooking spray; place 2 sandwiches in skillet. Cover and cook over medium-low heat 2 minutes on each side or until bread is golden brown and cheese is melted. Repeat with remaining 2 sandwiches.