Gather all ingredients and equipment.
For the Bread
Preheat broiler or grill to 350°F (180°C).
Slice the rolls on the bias into 1/2-inch-thick pieces.
Brush the slices with the olive oil and set aside.
For the Mussels
Place the olive oil in a large skillet or Dutch oven over medium high heat.
For the Mussels
Heat the olive oil in a large deep skillet over medium heat. Add the onion and sauté for 3-5 minutes or until translucent.
Add the tomatoes and cook until they begin to soften and burst open.
Add the garlic and sauté for an additional minute.
Add the mussels, white wine, beans, salt, and pepper. Cover the skillet and steam the mussels until they start to open, about 4-5 minutes.
Turn off the heat, add in the butter, basil, and lemon zest. Stir to incorporate. Discard any mussels that did not open when cooking. Cover to keep warm.
Grill the slices of baguettes on either side until golden brown, about 1 minute per side.
Serve the grilled bread with the mussels.