1. Preheat grill to high heat for at least 10 minutes while you prepare the packets.
2. Cut two large pieces of heavy-duty aluminum foil, each approximately 12" square. Make a crease across the center of each — you will fold the foil pieces in half here once they are filled to create packets for the grill.
3. To prepare the zucchini, trim the ends and, using a mandoline or sharp knife, thinly slice the zucchini lengthwise, creating 8 to 10 long thin “ribbons.”
4. For the topping, thinly slice the white and light green portions of the scallions, discarding the green tops. Roughly chop the olives and sundried tomatoes together. Roughly chop the basil leaves. Stir the scallions, olives, tomatoes and basil together, then season with the zest of half a lemon.
5. To assemble your packets, double over the zucchini pieces, placing the pieces side-by-side to create a bed for the fish portions in the center of the front halves of the foil. Drizzle the zucchini with olive oil and season to taste with salt and pepper.
6. Lay the fish portions atop their zucchini beds, then top each portion with half of the olive and sundried tomato mixture.
7. To finish the packets, fold the back half of the foil along the crease over the veggie-topped fish and fold over the long end to close, then fold over each side to completely close the packets. For a sturdier seal, fold each side once more.
8. Grill the packets on high heat with the grill lid closed for 10 minutes.
9. To serve, place the fish portions on a large plate, then add the zucchini pieces as a yummy side dish.