I am a fan of roasting whole fish instead of fillets as I believe cooking anything on the bone, be it chicken, lamb, steak, or fish, improves the flavor, but you could roast fillets instead, simply adjusting the cooking time to about two minutes less.
I love tahini with grilled fish; its creamy and rich texture pairs really well with grilled flavors. I just pool it underneath the whole mackerel and drizzle a little more over simple roasted carrots that go with the fish. It would be delicious over some steamed potatoes as well. I always think fresh herbs brighten all the flavors of a dish, and here, I use cilantro. —Sara Jenkins
For the Fish
whole boston mackerel, gutted (about 3/4 to a pound, each)
Make the tahini sauce: Finely mince the garlic clove in a food processor. Add the tahini and lemon juice and blend. The tahini will thicken and you should thin it out to a pourable sauce consistency with the water, adding 2 tablespoons of it at a time. Taste and add salt to your taste. Reserve at room temperature. (The sauce will keep well refrigerated for a week or so.)
Scrub the carrots clean and trim the tops, leaving a small tuft of the green tops. Set aside.
Preheat the oven to 450° F. Stuff the mackerel cavities with the lemon, parsley and thyme sprigs. Season generously with salt and pepper. Lay the fish out in a single layer on a roasting pan and season with salt and pepper. Pour the olive oil over the fish. Roast for about 10-12 minutes until the fish is blackened and blistered, and the fish is cooked through to the bone. (I always use the old fashioned rule of cooking fish 10 minutes an inch, and it rarely lets me down).
Meanwhile, blister the carrots in a hot pan with the olive oil and salt and pepper, until the carrots brown and look cooked.
To serve, pool the tahini at the bottom of the plate, reserving a 1/4 cup. Place the mackerel on top and then add the carrots. Drizzle the remaining tahini sauce on top and garnish with sesame seeds and cilantro sprigs. Serve with lemon or lime wedges if desired.