For the Lemon Aioli: Mix together all the ingredients in a small bowl. Set aside.
For the Swordfish Panini: Warm the olive oil in a large, heavy skillet over medium-high heat. While the pan heats, season the fish with salt and pepper. Rub the herbs de Provence and minced garlic all over the fish. Cook the fish in the skillet until just cooked through and golden, about 2 to 3 minutes per side, depending on the thickness of the fish.
Cut the bread into 4 sandwiches that will accommodate the size of the fish fillet. Cut the bread in half to make a top and bottom for the sandwich. Spread the Lemon Aioli on both halves of the sandwich. Top the bottom half with a handful (about 1/2 cup) of arugula greens. Top the arugula greens with the cooked swordfish, and top the sandwich with the remaining bread.