Preheat your panini press or heat a grill pan over medium-low heat.
Spread 1 Tbsp / 15 ml of tapenade on each of the four slices of bread.
Place the mozzarella slices over the tapenade on all slices.
On two of the bread slices, which will be the bottom halves, layer the tomato slices and top with the baby spinach.
Close the sandwiches with the remaining mozzarella-topped bread slices.
If using a panini press, place the sandwiches inside, close the lid, and cook until the inside is hot and the cheese is completely melted, about 4-6 minutes.
If using a grill pan, place the sandwiches in the pan and set a heavy skillet on top to gently press them down.
Cook for 2-3 minutes until the bread has grill marks.
Flip, place the skillet back on top, and cook for another 2-3 minutes until the cheese is fully melted.
Serve immediately.
Pat the fresh mozzarella and tomato slices with a paper towel to remove excess moisture and prevent a soggy sandwich.
Add a sprinkle of dried oregano or a few fresh basil leaves for an extra layer of Italian-inspired flavor.
