How to Make It
In a blender, combine the tomatoes with the vinegar, 1 tablespoon of the oil, 1/4 teaspoon of the oregano, 1/4 teaspoon pepper, and 1/2 teaspoon salt. Pulse to combine, leaving small chunks of chopped tomato. Don't puree or the vinaigrette will be too frothy.
In a large saucepan, heat 1 tablespoon of the oil over moderate heat. Add the scallions and fennel and cook, stirring, for 2 minutes. Stir in the squash, the remaining 1/4 teaspoon oregano, and 1/4 teaspoon pepper. Cover and cook for 4 minutes. Add the broth and bring to a simmer. Stir in 1 teaspoon of the salt and the couscous. Cover. Remove the pot from the heat and let the couscous stand for 5 minutes. Fluff with a fork.
Meanwhile, in a large nonstick frying pan, heat the remaining 1 tablespoon oil over moderately high heat. Sprinkle the swordfish with the remaining 1/4 teaspoon salt and 1/8 teaspoon of pepper. Add the fish to the pan and cook for 3 minutes. Turn and cook until golden brown and just done, 2 to 3 minutes longer for 3/4-inch-thick steaks. Serve the swordfish on the couscous and top each steak with tomato vinaigrette.