In saucepan, melt margarine over medium-high heat; cook onions and garlic until softened, about 3 minutes. Add tomato and pinch each of the salt and pepper; cook for 1 minute.
Add vegetable stock and bring to boil; stir in couscous. Cover and remove from heat; let stand for 5 minutes. Fluff with fork. Stir in 2/3 cup of the Gouda cheese, basil, parsley and oregano.
Meanwhile, trim ends off zucchini; slice lengthwise in half. Using melon baller or spoon, scoop out pulp, leaving scant 1/2-inch (1 cm) thick walls. Sprinkle with remaining salt and pepper.
Divide couscous mixture among zucchini; sprinkle with remaining cheese. Place on baking sheet and cover with foil; bake in 400°F (200°C) oven until fork-tender, 25 to 30 minutes.