Hi and welcome,
You need to test immediately before you eat and again 2 hours after your first bite. Keep a food diary including portion sizes, and record your levels alongside. Try to keep the rise from before to after under 2mmol/l and preferably under 1.5mmol/l.
You can also test around 90 minutes after first bite if you want to catch your peak, or at 2.5hours after to make sure you are well on the way down.