2 medium-size red onions, cut into 1/2-inch-thick rounds
2 red bell peppers, quartered lengthwise, seeded
4 zucchini or yellow crookneck squash, cut on diagonal into 1/2-inch-thick slices
2 large portobello mushrooms, dark gills scraped away, quartered
1 head radicchio, cut into 6 wedges
6 tablespoons (3/4 stick) butter
6 small garlic cloves, minced
2 teaspoons dried tarragon
3 tablespoons dry white wine
1 tablespoon olive oil
Lemon wedges