Preheat the oven to 350 degrees F. Butter a 9-by-13-inch baking dish. Crush the tomatoes into the dish and add 1 cup of the reserved juice. Sprinkle with the brown sugar, garlic, parsley, tarragon, 1 teaspoon salt, 1/4 teaspoon pepper and the red pepper flakes.
Cut the white and light green parts of the scallions into 2-to-3-inch pieces and add to the tomato mixture. Roughly chop about 1 cup of the scallion greens and add to the dish along with 1/4 cup water. Dot with 2 tablespoons butter, cover with foil and bake until the scallions are tender, 35 to 40 minutes. Uncover, increase the oven temperature to 450 degrees F and bake until the sauce is thickened, about 20 more minutes.