Sensitivity to insulin often varies by time of day. I have a different insulin to carbohydrate ratio for each meal. It could just be that you have become more sensitive to insulin at lunchtime and therefore need to take less.Try using a different insulin to carbohydrate ratio eg if you normally take one unit per 10g carbs try taking one unit per 15g carbs instead. Another cause of the hypos could be if you are exercising around that time but you don't mention that in your post. The most likely reason for the hypos occurring an hour after your lunch is that this is roughly when the insulin is peaking.