Prepare BBQ spaghetti or use leftovers.
Place 1 slice of cheese onto each piece of bread. Add spaghetti and assemble sandwich.
Heat a skillet or griddle over medium-high heat.
Brush outside of 1 bread slice with melted butter.
Spray pan with cooking spray and add sandwich, buttered side down. Cook 2-3 minutes, until bread is golden brown and crispy.
Brush melted butter onto top bread slice before flipping. Continue to cook another 2-3 minutes on other side.
Slice, serve warm, and enjoy!