Roasting summer produce--eggplant, tomato, zucchini, and peppers--on a baking sheet on the grill yields silky, melt-in-your-mouth vegetables. We tuck them into pita pockets with or without chunks of skewer-grilled lamb. Prep and Cook Time: 1 1/2 hours, plus at least 3 hours marinating time. Notes: Vegetables can be grilled a day ahead and refrigerated, covered. Allow to come to room temperature and toss in feta and walnuts before serving. If you're using regular-size pitas, this filling makes enough for 4 or 5.