In a large saute pan over medium heat, add the olive oil, scallions, garlic, a nice pinch of salt and a few grinds of black pepper. Cook until the greens of the scallions are wilted and darkened with the oil and the garlic is tender and slightly golden, about 4 minutes. Add the tomatoes, season with salt and cook while stirring until the tomatoes are softened, about 2 minutes. Add the clam juice and lemon juice, bring to a light simmer and stir. Taste, and if the tomatoes and lemon juice are too tart, add sugar and stir.
Sprinkle the shrimp with salt and pepper and add to the pan. Cook on 1 side until the shrimp begins to turn opaque and curl slightly, 2 to 3 minutes. Then toss and cook until they just begin to turn pink on the other side, 1 to 2 more minutes. (Shrimp cooks fast and there's a thin line between done and overdone; the best rule is to remove the pan from the heat as they begin to reach the finish line. Continue tossing and the heat of the pan will continue to cook them until done.) Serve warm or chilled.