Prepare the bread: Lightly brush one side of each slice of bread with olive oil or softened butter. This will help the panini get that golden, crispy crust.
Assemble the panini: On the un-oiled side of two of the bread slices, spread a thin layer of pesto or tapenade.
Layer the ingredients: On top of the pesto/tapenade, layer the mozzarella, tomato slices, roasted red peppers, and sliced olives.
Close the sandwich: Place the remaining two slices of bread, oiled-side up, on top of the fillings.
Cook the panini: Using a panini press: Place the panini in the preheated press and cook for 3-5 minutes, or until the cheese is melted and the bread is golden brown. Using a skillet: Heat a skillet over medium heat. Place the panini in the skillet and use a heavy object (like another pan or a foil-wrapped brick) to press down on the sandwich. Cook for 3-4 minutes per side, or until the bread is golden and the cheese is melted.
Serve: Once cooked, remove from the press or skillet, slice in half, and enjoy immediately!