Any tips on not getting high peaks when eating a lot of carbs?

So I've been eating low carb basically since I've gotten type 1 diabetes little over 2 years ago, and now recently I've been wanting to start eating more vegan which means more carbs. I've started with oatmeal in the morning and when I eat it I get some insane peaks. It usually goes up to around 12 mmol/L(216mg/dl) and then down to the good area around 5 mmol(90mg/dl) really quickly. I'm guessing I'm taking the right amount of insulin since it goes down to good level afterwards. I tried with taking my rapid acting insulin around 10-15 minutes beforehand but it doesnt do anything, I otherwise take it right before a meal. I've never had to deal with anything like this before since my low carb diet bascially doesnt give me peaks. Any tips?

Might add that " a lot of carbs" are around 50 for me.