How to Make It
Combine all Marinade ingredients in a 1-gallon ziplock plastic freezer bag. Add Vegetables. Gently massage bag until all vegetables are coated in marinade. Seal bag, squeezing out excess air. Lay bag flat on a small rimmed baking sheet, and place in refrigerator. Chill 2 hours, turning bag once or twice.
Remove from refrigerator, and let stand 20 minutes.
Preheat grill to medium-high (400°F to 450°F). Remove vegetables from marinade, reserving marinade. Remove any peppercorns that have stuck to the vegetables. Season with salt and pepper to taste, if desired. Grill vegetables, uncovered, until slightly softened and grill marks appear, about 5 minutes per side. (Try not to move vegetables around too much.) Tomatoes may take less time depending on their size.
Pour reserved marinade through a fine wire-mesh strainer into a bowl; discard solids. Drizzle grilled vegetables with marinade.