1. In a 4- to 5-quart pan over medium-high heat, stir bacon often until browned around the edges, 3 to 4 minutes. Add onion and stir often until onion is limp, about 5 minutes.
2. Stir in milk, mashed potatoes, turkey, corn, cilantro, and pepper. Bring to a simmer and cook, stirring frequently, until soup is hot and slightly thickened, about 10 minutes. Add salt to taste. Ladle into bowls and serve immediately.