Short version, is probably avoid processed food (e.g. Doritos and Pringles). Ditto Parmesan and deli meats (so that’s Subway out, unless you get veggie subs). Tomatoes too. And miso and green tea and shiitake mushrooms and kimchi and cheddar. Um, maybe don’t eat out. I don’t know how much you can rely on avoiding 味精 on the ingredients list, because it may just be “invisibly” listed under other seasonings.
Damn, I didn’t realize it was that tough to avoid. That’s a bugger of an allergy.
A few other threads, from here and elsewhere, that may be helpful: