I quite often eat muesli with full fat greek yogurt and a sprinkling of mixed seeds. This gives me a balance of carbs, fat and protein and I have learned over the years to adjust how much insulin I need for my normal portion.
Now, if you are being told to take a fixed dose of insulin at the moment, and it’s not working how you’d like, the only option for you is to adjust the balance of carbs, fat and protein to reduce or increase the carbs a bit, depending on whether the insulin seems too much or too little. You can do this whatever your normal breakfast is, I just used mine as an example. If my Blood glucose was too high after breakfast, I'd have a bit less muesli with a few more seeds and an extra spoonful of yogurt the next day. If I was finding my levels too low, I’d increase the muesli, etc etc.
You just need to experiment a bit with the balance of what you normally eat.