Hello. I am afraid I know nothing about your growing conditions other that that you are frost free and being an island don't have large variation in temperature. Since you mentioned kohlrabi. It is a cool weather crop. If you summer temps reach 30 degrees Celsius. You plant to avoid maturity during midsummer. You could grow during winter, spring, or fall. That applies to all the cole crops. Broccoli, cabbage, cauliflower, turnip …
The travel folks make Zakynthos sound an island paradise. But they don't give a lot of info about normal daily life.