1Heat closed contact grill or panini maker for 5 minutes. Meanwhile, spread 1 side of each bread slice with honey mustard; sprinkle onions over 4 slices of bread. Layer with spinach, roasted peppers, cheese and remaining bread slices.
2Place sandwiches on grill. Close grill; cook 2 to 3 minutes or until bread is toasted and cheese is melted. Cut each sandwich in half to serve.