Solids??

So we started my son on oatmeal a week ago. I’m wondering how we begin introducing other foods as well. Do we stop the oatmeal and start another or should we do one at lunch time and one at dinner time. I was going to try avocados. I know you have to stick to eat food for 4 days to make sure there’s no allergies but I’m just wondering if I should continue the oatmeal and add the other fruits or vegetables as another meal