Soak the bluefish for 10 minutes in 1 quart of ice water and 2 tablespoons kosher salt. Drain. Pat dry. Heat grill (charcoal preferred) to very hot.
Toss together the tomato salad ingredients. Let sit for one hour.
Make the polenta. Simmer milk and chicken stock. Season with salt and pepper. Add garlic. Whisk in polenta. Reduce. Heat. Simmer until thickened and polenta is soft, not crunchy. Season.