Slice the zucchini in half lengthwise, then use a spoon or melon baller to hollow out the centers. Discard the flesh or save for another use. Lightly brush the zucchini with olive oil, then place cut side up on a baking dish or sheet. Sprinkle lightly with salt and pepper. Bake for about 20 to 22 minutes, or until tender. Remove from the oven, then turn on the broiler.
For the filling:
While the zucchini is baking, add the broth to a small saucepan. Bring to a boil, then stir in the couscous. Remove from the heat, cover and let sit for 5 minutes. Fluff the couscous with a fork, then add to a medium bowl and let cool for about 5 minutes.
To the bowl, add in the garlic, tomatoes, ¼ cup of the basil, the olive oil, salt and pepper. Mix to combine.
Scoop some of the filling into each of the baked zucchini. Sprinkle the tops evenly with the mozzarella. Return to the oven and broil for about 3 to 5 minutes, until the cheese is melted. Sprinkle with the remaining basil and drizzle generously with balsamic glaze.
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