We are all different, so what you can eat (carbs) will be more than I can eat. Being a T2 I dont eat oatmeal, way to many carbs (carbohydrates) in oatmeal
Carbs raise BG not just sugar... ALL carbs raise BG.
If you must eat oatmeal "test BG , count carbs eat, test BG, revue"
The best way to start your day is with a meal that wont take your BG up above the threshold of where damage starts. That is a BG of 140. above that is where damage to your nerves and capillaries start. That is why I say test if you dont know your BG how can you know if the oatmeal is raising your BG to high?
if you want to check, then measure a known amount of steel cut oats (not instant type) and cook it with water. You can then add milk and / or cream, but no sugar. Measure your blood sugar 2 hours after eating. If your blood sugar is < 140 (or even better less than 120) then you know you can eat that amount of oatmeal. If your blood sugar is higher than 120/ 140, then you could try eating a lesser amount the next time you try it.
Some people with diabetes find they can eat oatmeal, others cannot.
I make mine with milk and it doesn't raise my blood sugar
I have a bowl of porridge every morning. I put 4 dessert spoons (slightly rounded) in a bowl and add 1 teacup of water. A few grains of salt. Put in microwave at medium setting for 2 minutes, remove, stir and microwave for one more minute. If the microwave power is too high, it may boil over. Next time adjust quantities, time and power to get a better result. Oats are supposed to be good because they are absorbed slowly, but speak to your dietician. As it's the first meal of the day, I add about
a quarter teaspoon of sugar(!), but it's the only sugar I add to anything all day.