How to Make It
In a medium saucepan, bring 5 cups of water to a boil with the sugar. Whisk in the polenta in a thin stream. Cook over low heat, stirring constantly, until thickened, about 5 minutes. Remove from the heat. Stir in 3 tablespoons of the olive oil and season with salt. Press a piece of parchment or wax paper directly onto the surface of the polenta and keep warm.
In a large skillet, heat the remaining 3 tablespoons of olive oil. Add the scallions and crushed red pepper and cook over moderate heat for 1 minute. Add the tomato paste and cook, stirring, until slightly darkened, about 3 minutes. Add the wine and 1/4 cup of water and simmer over moderately high heat for 1 minute. Add the shrimp and simmer, stirring, until just cooked through, about 2 minutes. Stir in the parsley, lemon juice and lemon zest and season with salt and pepper. Remove from the heat.
Rewarm the polenta over moderately high heat, whisking constantly. Spoon a pool of polenta in the center of 8 shallow bowls. Spoon the shrimp and sauce over and around the polenta and serve right away.