If your results are higher in the morning than when you went to bed, it may be because your liver starts pumping out glucose from 3am onwards. This may be for one of two reasons.
1. It's gearing up for the day ahead. A carby snack before bed isn't going to help. A protein snack may, if your body digests it very slowly and manages to convince the liver not to churn out so much glucose.
2. You are dropping low in the night, so your liver is pumping out extra glucose to compensate, and overreacts, so you end up higher. The only way to check this is by setting an alarm for 3am and testing then, to check you're not hypo. If you are dropping low, then a slow release carby snack before bed may help.
If you are on Metformin only, 2 shouldnt occur, so it's probably 1.
Banana tends to be quite quickly absorbed, so may give you a glucose spike in the first part of the night. Again, testing is the only way to find out,( about an hour after you've eaten it, I should think, is when you're likely to see a spike from it, but people vary)
Most people who have to live with the Dawn Rise tend to find they can stop it in its tracks by getting up and having breakfast, ( preferably low carb, or slow release) when the liver thinks, OK, job done, and eases off.