Trim the eggplant ends and cut into 1/4–1/2-inch slices. Arrange on a tray, sprinkle both sides lightly with 1/2 teaspoon salt and let sit 10 minutes to draw moisture. Pat dry with paper towels.

Season tomato

Slice tomatoes about 1/4-inch thick. Drizzle with 1 teaspoon olive oil and 1 teaspoon balsamic vinegar (optional). Lightly season with 1/4 teaspoon salt and a grind of black pepper. Set aside.

Prepare mozzarella

Slice buffalo mozzarella into 1/4-inch thick slices or tear into pieces. Pat dry on paper towels to remove excess moisture so sandwich won't get soggy.

Cook Eggplant & Warm Peppers

Heat a large nonstick skillet or grill pan over medium-high heat. Add 1 tablespoon olive oil and swirl to coat. When hot, add eggplant slices in a single layer (work in batches if needed). Cook 2–3 minutes per side until golden brown and tender. Transfer to a plate and season lightly with remaining 1/2 teaspoon salt and a pinch of pepper.

If roasted red peppers are cold from the jar, warm them briefly in the same pan for 1 minute per side with a drizzle of olive oil to take chill off and concentrate flavor; transfer to plate with eggplant.

Assemble Sandwich

Slice the ciabatta horizontally to create a top and bottom. If the bread is thick, you may remove some interior crumb to make for even pressing.

Spread a thin, even layer (about 3 tablespoons) of pesto on the bottom half of the bread and 1–2 tablespoons on the top half.

Layer components evenly over the bottom bread in this order: half the mozzarella, half the tomato slices (overlap slightly), half the warm eggplant slices, half the roasted red peppers. Season lightly with remaining salt and pepper between layers as desired. Repeat with remaining mozzarella, tomato, eggplant and roasted peppers to build two stacked layers (the "5 pieces" are mozzarella, tomato, eggplant, roasted red pepper, and pesto). If using optional cheese, add it on top of the mozzarella layer.

Top with the bread lid and press gently by hand to compress layers.

Press and Finish

Preheat a panini press according to manufacturer instructions. If you don't have a panini press, heat a large heavy skillet (cast iron) over medium and have a second heavy skillet or a foil-wrapped brick ready to press.

Brush the exterior cut faces of the sandwich lightly with remaining 1 tablespoon olive oil or the butter/olive oil from the Grill/Finish section. Place sandwich in the press or in the hot skillet. If using skillet-only, place the second heavy pan or weighted object on top to press.

Grill/press for 4–6 minutes until bread is golden and crisp and cheese is warmed and slightly melty. Flip once if using skillet and press each side 2–3 minutes. Monitor to avoid burning; reduce heat if outside browns too fast before cheese warms.

Remove from heat and let rest 1–2 minutes to settle. Cut into 4 generous pieces (or 6 smaller) and serve immediately.