Prep ingredients and equipment: Drain the tuna thoroughly and place in a mixing bowl; rinse and drain the canned cannellini beans; drain the capers and roughly chop. Line a plate for assembly and preheat a panini press or heavy skillet over medium-high heat. (Why: good drainage prevents a soggy filling; preheating ensures the bread crisps quickly and the filling warms through without overcooking.)

Coarsely mash the beans: Place the rinsed cannellini beans in a small bowl and use a fork or potato masher to smash them lightly — leave some whole beans for texture. (Why: smashing creates a creamy binder so the tuna mixture holds together like a spread, while leaving some whole beans provides pleasant bite and contrast.)

Combine tuna and beans: Flake the drained tuna into the bowl with the mashed beans. Add the roasted garlic aioli and chopped capers. Fold gently until combined — don’t overwork it. Season with a pinch of salt and a generous grind of black pepper. Taste and adjust: because tuna and capers can be salty, add salt slowly. (Why: folding keeps some larger flakes of tuna intact for texture; aioli adds richness and helps emulsify the mixture so it won’t fall out of the sandwich.)

Prepare the bread: Brush the cut sides of each ciabatta slice lightly with 1 tsp olive oil (or spread a thin film of butter if you prefer richer flavor). (Why: a light fat prevents the bread from drying, encourages even browning and helps create a golden, crisp crust when pressed.)

Assemble the panini: On the bottom slice, spread the tuna–bean mixture in an even layer, leaving a small border so filling doesn’t spill when you press. Top with the romaine leaves (pat dry — excess water = soggy bread). Finish with the top slice. (Why: layering the lettuce directly on the filling keeps it from wilting too quickly and provides a fresh crunch.)

Grill the sandwich: Place the sandwich in a preheated panini press and cook 4–6 minutes until the bread is deeply golden and the filling is warmed through. If using a skillet, place the sandwich in the skillet and press with a heavy pan or cast-iron skillet; cook about 3–4 minutes per side over medium heat, then press and rotate until evenly browned. (Why: high, dry heat creates Maillard browning for flavor; pressing compresses the sandwich so the interior warms quickly and the exterior crisps.)

Rest and cut: Remove the panini and let it rest for 1–2 minutes before cutting in half diagonally. This short rest allows the filling to set slightly so it won’t all spill out when you cut. Serve immediately with an extra grind of black pepper. (Why: resting improves presentation and makes it easier to handle; the panini is best eaten hot and crisp.)