The Dinner Lady Detectives by Hannah Hendy

Margery and Clementine are lunch ladies, though Clementine prefers their actual title which is Education Center Nourishment Consultants.  Their job is to prepare and serve lunch to the students at Summerview Secondary School.

Their peaceful existence is shattered when their manager is found dead in a walk-in freezer.  While the police are convinced that the manager’s death was an accident, Marjorie and Clementine are less sure- especially after the freezer door mysteriously locks behind them after they’ve decided to take a peek at the scene. They managed to escape the freezer, but as they continue to investigate the matter of their manager’s death, it begins to seem that now someone is out to kill them!

This is a fun British cozy mystery and apparently the first of a series.