Preheat the oven's broiler. Place the fish fillets in a shallow oven-safe dish. In a small bowl, combine the mayo, garlic, thyme, lemon zest, salt and pepper and mix well with a fork. With a pastry brush or a fork, spread half the mixture on one side of the fish, then turn the fillets over, and brush with the rest of the mixture. Put the fish under the broiler for about 8 minutes, until it is just done inside and getting opaque and flaky. Do not overcook.