Lightly brush green and yellow peppers, onion, tomatoes, and eggplant with the 1 tablespoon olive oil. Place peppers, onion, and eggplant on greased grill rack of an uncovered grill directly over medium coals. Place tomatoes in 2 foil pie plates. Place pie plates on grill rack directly over coals. Grill onion slices, uncovered, for 10 to 15 minutes; sweet peppers for 8 to 10 minutes; eggplant for about 8 minutes or until vegetables are tender, turning occasionally. Grill tomatoes for 10 to 15 minutes or until heated through, turning once. Remove vegetables from grill. Cut vegetables into bite-size pieces.
Meanwhile, bring water to boiling in a medium saucepan. Add basil and/or oregano, the 2 teaspoons olive oil, and salt. Stir in couscous. Cover and remove from heat. Let stand 5 minutes or until liquid is absorbed. Sprinkle with nasturtiums.
Fluff couscous with a fork. Place on a serving platter and top with grilled vegetables. Makes 6 to 8 side-dish servings.