In a large skillet, melt the butter over medium heat. Add the scallion whites, season with salt and pepper and cook, stirring, for 2 minutes. Add the corn, lima beans and cream and bring to a boil. Stir in the chicken and cook, stirring occasionally, until the sauce is thickened, 4 to 5 minutes. Stir in the tomato and scallion greens just before serving.