1. Preheat oven to 400 degrees F. In 13 by 19 inch baking dish, combine lemon zest, 1 TBSP oil, and onion, reserving 1 TBSP of the oil. Spread in even layer. Roast until onion is tender, stirring occasionally, about 15 minutes.
2. Remove from oven. Stir in zucchini, squash, and garlic. Return to oven and roast 10 minutes. Remove from oven.
3. Increase oven temperature to 450 degrees F. Push vegetables to one side and add fish. Spoon vegetables over fish.
4. Return to oven and roast until fish is opaque in venter, 8-10 minutes for thin and 12-15 for thick.
5. Meanwhile, combine vinegar, remaining oil, water, mint leaves, and remaining onion. Spoon over bass fillets and serve.