I can only say what worked for me. As soon as I get up, before getting dressed or anything else, I have a coffee with double cream. I try to avoid any strenuous exercise in the mornings. I just have a walk towards lunch time. I sometimes have a cup of tea mid morning. Other than that, just water. Since starting this several months ago I have seen my lowest ever pre-lunch levels.
I had previously tried a boiled egg. That didn't work.
Previous to that I had breakfast of full fat yogurt and a very few berries. That made it worse.