Preheat the oven to 425F. If you’re using a turbo broiler, there is no need to preheat.
Sprinkle the fish with salt and pepper.
In a bowl, whisk together the mayo, cream cheese and garlic. If the cream cheese has been sufficiently softened, the mixture should be smooth.
Melt half of the butter in a frying pan. Pan fry the fish on both sides just long enough for it to change color. You want it half cooked only at this stage because you’re still going to bake it. If you cook it through in the frying pan, the fish will overcook during baking and turn dry. So, half cook the fish then transfer to a baking dish.
Turn off the heat. Add the rest of the butter and swirl. Add the vegetables and stir to coat each piece with butter.
Scatter the vegetables around the fish in the baking pan.
Spread the cream cheese and mayo mixture evenly on top of the fish. Bake for 12 minutes or until light brown spots form on the topping.
Remove the baking dish from the oven. Let the fish rest for at least five minutes before cutting and serving to allow the topping to firm up a little.