Complex sentence: During a lunch period when Dr. Hoyer was on lunch monitor duty overseeing the students during lunch, some students decided to eat outside due to the fair weather, since the cafeteria at the school has access to an outdoor eating area.
Split into simpler sentences: During a lunch period which Dr. Hoyer was on lunch monitor duty, overseeing the students during lunch. Some students decided to eat outside due to the fair weather, and the cafeteria at the school has access to an outdoor eating area.