Heat olive oil in a large skillet over medium high heat. When oil is hot, add chicken and cook, stirring occasionally, until no longer pink on the outside, 4 to 5 minutes.

Add mushrooms and continue to cook, stirring occasionally, until chicken is lightly browned and no longer pink in the center. Stir in milk, condensed soup, pimentos, onion powder, and black pepper.

Bring the mixture to a boil. Cover skillet and reduce heat. Simmer until the sauce is hot and slightly thickened, 2 to 3 minutes. Stir together and serve.