I used a CGM recently. I tried breakfast as oatmeal with blueberries and mixed in with peanut butter. It spikes my blood sugar outside the "normal range". I treat oatmeal as once a week treat to avoid food boredom.

The oatmeal was a "big bowl" variety from a packet. I heard rolled oats might be better but it's a hassle to cook.

Most days breakfast is scrambled eggs (3 eggs), spinach, cheese. Sometimes I add tuna or avocado for variety. That keeps things stable.