Prepare couscous according to package directions. Cut tops off peppers. Remove stems from tops and seeds from peppers. Dice tops.
In nonstick skillet, heat olive oil over medium-high heat. Add onion and cook until soft, about 5 minutes. Add diced pepper tops and zucchini; cook, stirring frequently, until soft, about 4 minutes. Add garlic and cook 30 seconds more. Stir cooked vegetables into prepared couscous.
Rinse peppers, place in glass baking dish, cover with plastic wrap, and microwave 9 minutes.
Spoon couscous mixture into peppers. Insert green onion for handle of stuffed pepper, if desired. Makes 4 servings.