Feeding baby

Okay, I’m thinking about starting my babe on some food. He is 19w 3d right now. I was thinking about starting with oatmeal. He’s where my problem is- I can’t remember what to do! My oldest is 9 and he’s the only other baby I’ve had, and I can’t remember how I did it when he was a baby. I read where you nurse them first then offer food. Do I feed baby breast milk first and then give him oatmeal? If I do that, won’t that stretch his stomach since he just ate what he normally eats? Or do I give him oatmeal first, and then nurse him? I feel like this is what most do, but then I’ve read to do it the opposite way.