Also be wary of any spice blends or pre-packaged foods. At least in the US, 99% of manufacturers are too lazy to look for any other flavor beyond onion/garlic. Its a real pain in the butt (lol)
Green onions are another good substitute. Just don’t use the white part and only chop up the green shoots.
As someone with massive gut issues who also cannot handle onions or garlic I found Bell Peppers to be my newest favorite flavoring for dishes. Once you get the overwhelming taste of garlic/onion out of the way the pepper’s complex flavors start to really shine through.
Also check out the Low FODMAP diet. Onions/Garlic are the main culprits to remove FODMAP from your diet and there are now lots of recipes available out there without them.
I’ll have to give tomatillos a try, thanks for the suggestion.