Preheat your panini press.  If you don’t have a panini press, you can still make this sandwich.  Grill it like you would a grilled cheese, but add a heavy skillet to the top of it while it is grilling.

In a medium pan, melt the butter over medium heat.  Add the spinach.

Stir until it wilts enough that you can’t believe you started with 2 cups (this should only take about a minute).

Stir in the artichoke hearts and sun-dried tomatoes.

Sprinkle the mixture with salt and pepper and stir until the artichoke hearts and sun-dried tomatoes are heated thoroughly.

Spread half of the mixture on one slice of bread and the other half on another.  Top each mixture with cheese, if using.

Close the sandwiches with the remaining two slices of sandwich bread.

Spray the outside of the bread with the olive oil cooking spray.  Cook the sandwiches in the panini press until it is crispy and the cheese is melted, about 2 minutes.  Slice in half and serve immediately.