Preheat oven to 400℉. Prepare shallow baking dish by spraying with nonstick cooking spray.
Slice top off tomatoes. Scoop out excess pulp and seeds. Place upside down on paper towels to drain any remaining liquid while you prepare stuffing.
In a large bowl, combine couscous, mozzarella, basil, Parmesan, garlic powder, salt and pepper.
Fill each tomato with stuffing mixture, pressing firmly. Place stuffed tomatoes in prepared baking dish.
Bake at 400ºF for 25 minutes or until tomatoes are tender and cheese is melted.
Serve immediately, drizzled with balsamic glaze and more fresh basil, if desired.
Notes
Gluten-free: Substitute cooked quinoa for the couscous.
Cheese options: If you can't find mozzarella pearls, you can use a ball of fresh mozzarella, chopped into small pieces. Try regular shredded mozzarella or another type of cheese instead of the fresh mozzarella, if you prefer.
Make ahead: Stuffed tomatoes can be completely prepared ahead of time, up to a day in advance, and refrigerated until ready to bake. Add about ten minutes to the baking time.