1: Place the tuna loin or steaks in a baking dish. Season all over with salt, pepper, and herbes de Provence. Drizzle with lemon zest and juice and extra virgin olive oil. Let marinate for 30 minutes while you light your grill and prep your vegetables.
2: Set up your grill for direct grilling and heat to high. For the best results, you’d work over a wood fire.
3: Meanwhile, insert toothpicks into the onion slices to keep them from falling apart on the grill. Brush both sides with olive oil and season with salt, pepper, and herbes de Provence.
4: Grill the peppers until the skins are blistered and darkly browned, 3 minutes per side, 12 minutes in all. Transfer to a cutting board and cut the pepper flesh off the core, discarding the stem and seeded core.
5: Grill the onion slices until darkly browned on both sides, 2 minutes per side. Transfer to the cutting board and discard the toothpicks.
6: Grill the tuna until sizzling and darkly browned on the outside, turning with tongs. Leave the inside blood rare. Transfer the tuna to a cutting board and cut into 1/2 inch slices.
7: Cut the rolls almost in half through the side. Pull out a bit of the soft interior so you have more room for the filling. Brush the cut sides with olive oil and toast on the grill, 1 minute.
8: Assemble the pan bagnats: Place a lettuce leave on the bottom half of each roll. Top with tuna slices, followed by the bell pepper, grilled onion, tomato slices, egg slices, olives, anchovies, and basil. Drizzle the olive oil over the filling and top bread slice and season the filling with salt and pepper. Close the sandwich and get ready for a tuna sandwich like you’ve never tasted.