Prepare the vegetables: trim the zucchini and cut into 1/4-inch thick lengthwise slices (you'll get about 6–8 slices). Cut the eggplant into 1/4-inch slices. Core and quarter the red bell pepper, remove seeds, and slice into large flat pieces. Uniform thickness ensures even cooking and consistent char.

Salt the eggplant slices and rest for 10 minutes: lay eggplant on a rack or paper towel, sprinkle about 1/2 tsp salt over the slices and let sit. This draws out excess moisture and any bitterness, prevents a soggy panini, and helps the eggplant brown better. After 10 minutes, pat the slices dry with paper towels and discard any collected liquid.

Preheat your grill pan or cast-iron skillet over medium-high heat (5–7 minutes). A very hot pan gives quick searing and attractive char marks without overcooking the vegetables; this concentrates their flavor.

Brush both sides of the zucchini, eggplant and red pepper lightly with 1 tablespoon olive oil, then season with 1/4 tsp salt, 1/4 tsp black pepper and the dried oregano. The oil helps the vegetables caramelize and prevents sticking; seasoning early layers flavor into the vegetables as they cook.

Grill the vegetables in batches: place the slices on the hot pan without crowding. Cook zucchini and eggplant 2–3 minutes per side until golden brown and tender with good char; cook red pepper 3–4 minutes per side until skin is slightly blistered and softened. Use tongs to turn once — frequent turning prevents a deep sear. Transfer grilled vegetables to a plate and keep warm.

Optional quick char on peppers under broiler: for more blistering, you may finish the pepper under a high broiler for 2–3 minutes, turning once, then place in a bowl and cover to steam for 5 minutes—this loosens skins for easy peeling. Peeling is optional; keeping skins adds color and nutrients.

Mix hummus with garlic (optional) and a pinch of pepper: in a small bowl combine the hummus, minced garlic (if using), and a pinch of salt and pepper. This builds a bright, aromatic smear that complements the smoky vegetables.

Assemble the panini: lay 4 slices of bread on a work surface. Spread about 1/4 cup (60 g) hummus on each bottom slice (this acts as a moisture barrier and flavor foundation). Layer 2–3 slices of zucchini, 2–3 slices of eggplant, and several pieces of red pepper evenly across each sandwich. Scatter about 1 ounce (28 g) of shredded or thinly sliced mozzarella (or dairy-free cheese) over the vegetables. Top with the remaining bread slices.

Brush the outside of each sandwich lightly with the remaining 1 tablespoon olive oil or spread 1/2 tsp butter on each outside slice. Butter or oil promotes even browning and crispness in the press or skillet.

Cook the panini: If you have a panini press, preheat it and grill the sandwiches 4–5 minutes until the bread is deep golden and the cheese is melted. If using a skillet, place a heavy skillet over medium heat and set the sandwich in the pan; press with a heavy cast-iron pan or another skillet (or use a lid) for even contact. Cook 3–4 minutes per side, flipping once, until bread is crisp and cheese melted. Pressing improves contact for a uniform crust and faster melting.

Rest and slice: transfer the panini to a cutting board and let rest 1–2 minutes before slicing on the bias. Resting allows juices to redistribute and the cheese to firm slightly so slices hold together beautifully.

Finish and serve: sprinkle an extra pinch of flaky salt or drizzle a teaspoon of balsamic reduction (optional) over the cut sandwiches for a bright finish. Serve warm.