In blender chop garlic. With motor running add oil in a steady stream; blend to nearly smooth, scraping sides. Brush both sides of bread with garlic-oil blend; sprinkle bread lightly with salt. In bowl toss chicken with salt, pepper, and half remaining oil. In second bowl toss vegetables with salt, pepper, and remaining oil; set aside.
For charcoal grill, cook peppers and eggplant on uncovered rack over medium-high heat 10 to 15 minutes, until tender; turn once. Add chicken and zucchini; grill 5 minutes, turn. Add bread and tomatoes; grill 2 to 5 minutes more, until chicken is no longer pink, vegetables are tender, and bread is toasted, turning as needed. (For gas grill, preheat grill. Set heat to high; cook food in same manner as above.)
Arrange all grilled vegetables and olives on platter; sprinkle olives with feta and oregano sprigs. Serve with Feta Vinaigrette. Makes 8 main-dish servings.
In a bowl whisk mustard, red wine vinegar, rice wine vinegar, garlic, oregano, salt, and pepper. Whisk in olive oil, by droplets then in a steady stream. To serve, stir in feta.