Preheat grill to medium-high heat.
Toss veggies (peppers, eggplant, onion, tomatoes) with seasoning: 1/4 teaspoon black pepper, 1 tablespoon oil, and 1/4 teaspoon salt.
Place peppers (skin side down) and onion on grill coated with cooking spray; grill 10 minutes. Turn onion; add eggplant to grill. Remove peppers. Place peppers in a zip-top bag; seal. Let stand 10 minutes.
Grill eggplant and onion 5 minutes; remove onion. Turn eggplant; grill 5 minutes. Remove eggplant. Add tomatoes to a grill basket (skewered tomatoes would work here, too); grill 5 minutes. Remove peppers from bag. Peel and discard skins.
Combine 1/4 teaspoon salt, vinegar, and sugar. Slowly add 2 tablespoons oil, stirring with a whisk. Combine vegetables, dressing, garlic, and olives. Sprinkle with 1/4 teaspoon salt, 1/4 teaspoon pepper, basil, and chives.