Position a rack in the middle of the oven and heat the broiler to high. Line a heavy rimmed baking sheet with foil.
In a small saucepan, bring 1 cup water and 1/4 tsp. salt to a boil over high heat. Remove from the heat and pour in the couscous. Stir once or twice with a fork and cover with a tight-fitting lid or foil. Set aside until the liquid is absorbed and the couscous is plumped and tender, about 10 minutes.
Meanwhile, core the tomatoes and cut them in half horizontally. Put them cut side up on the baking sheet and season generously with salt and pepper. Drizzle with 2 Tbs. of the olive oil and sprinkle with half of the garlic and half of the herbs. Broil the tomatoes on the middle rack of the oven for 4 minutes. Sprinkle the tomatoes with the feta and continue to broil until the feta turns a blistery brown, another 4 to 7 minutes.
Remove the cover from the couscous and fluff the grains with a fork. Stir in the remaining herbs, garlic, and 3 Tbs. olive oil, along with the olives, lemon zest, and lemon juice, until well blended and fluffy. Season with salt and pepper. Spoon the couscous onto a plate and set the tomatoes alongside. Serve immediately.