How to Make It
Light a grill or heat a lightly oiled grill pan. In a bowl, toss the fennel wedges with 2 tablespoons of the olive oil and season with salt and pepper. Brush the onion slices on both sides with 1 tablespoon of the olive oil and season with salt and pepper. Grill the fennel and onion over a medium-hot fire for about 4 minutes per side, or until lightly charred and just tender. Alternatively, cook the fennel and onion in the grill pan over moderate heat for about 5 minutes per side.
Lay two 2-by-3-foot pieces of heavy-duty foil on top of each other and put the tomatoes in the center. Add the grilled fennel and onion slices and season the vegetables with salt and pepper.
In a small bowl, combine the vinegar, lemon juice, garlic and mustard and blend in the remaining 2 tablespoons of olive oil. Spoon the dressing over the vegetables, then seal the foil package.
Set the vegetable package over a medium-hot fire and grill for 5 to 7 minutes, or until bubbling inside. Alternatively, set the package in the grill pan and cook over moderate heat for 5 to 7 minutes. Remove from the heat and let stand for 3 minutes. Carefully open the foil and sprinkle the vegetables with the basil and mint. Serve hot or warm.