Reserve 2 tablespoons sliced scallion tops for garnish. Cook and stir remaining scallions in the vegetable oil in a medium sized saucepan over medium heat for 1 minute.
Stir in flour until smooth. Gradually stir in milk; cook, stirring until mixture thickens and boils. Cook and stir for 1 minute more.
Add lobster, half and half, sherry, white pepper and salt. Cook and stir until heated through. To serve, ladle soup into bowls. Garnish with reserved scallion tops.
