I too had to heal my gut.
For over 10 months I survived on homemade chicken soup with chicken only. A few months later I did use celery after removing all of the fiber strings then chopped very fine along with some onion and then cooked it down almost in a predigested form.
The next vegetable that I added back months later was well cooked broccoli florets with all woody stems removed. Later I could have very young and tender green beans but I had to toss them if they had any fibrous strings at all.
I waited a full year before eating any raw salads.
It was my gut guiding me because there really is no info in dealing with this. All I could ever find on-line said to eat more fiber which would have killed me...