1. 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.
2. 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.
3. 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.
Wine Recommendation: Red wine with fish? When it's a fatty fish such as swordfish and the wine is pinot noir, the combination can't be beat. To see just how well it works, try an Oregon pinot noir, brimming with fresh red berries and subtle earth tones.