Combine relish, orange juice, and sugar together in a small bowl.
Spray large non-stick pan or grill pan with cooking spray; heat over medium-high heat. Add bread slices to pan. Layer with cheese, turkey and spinach, dividing ingredients equally between two bread slices. Spread relish mixture on remaining bread slices.
Cover over medium-high heat until cheese begins to melt. Assemble into two sandwiches. Cook one additional minute until toasted. Serve immediately.
Send your little ones to school with this nutritious and easy lunch box meal - a Cuban-Syle Grilled Turkey Sandwich