Here's a list of foods and tips:
And here's a cookbook!
I have gotten a lot of use out of this cookbook: Low-Fodmap and Vegan: What to Eat When You Can't Eat Anything https://www.amazon.com/dp/1570673373/ref=cm_sw_r_cp_api_i_NDSxCb138AMJY
What I found I miss most are sauces and this book has some good ones.
Edit for more detail: Partner has IBS. He was vegan for a year, which was really tough because it involved preparing literally all food. Now he's mostly vegan but eats eggs and occasionally fish.
Veg-wise, we mostly have potatoes, carrots, bell pepper, zucchini, and green beans. I just made an amazing pasta dish where you julienne carrots, bell pepper, and zuchhini and sautee them, then toss with homemade parmesan (garlic oil, walnuts, nutritional yeast, salt in a food processor) and the herbed tempeh nuggets from that book I linked. SO GOOD!
Roasted fingerling potatoes, carrot, and zucchini tossed with Thyme, Olive Oil (garlic infused or not), and nutritional yeast (and salt/pepper ofc) is good as well.
There's a really good Indian-style chard, potato, and carrot recipe in that book as well. We make seitan "chicken" balls (they're just shaped like balls, we call them chicken balls lol) that go really well with them.
You can totally be vegetarian and low fodmap, even vegan and low fodmap. It does mean eating out a bit less and preparing more of your own food. But it's definitely doable.
For processed foods: If you're in U.S. you might try the Potato and Pea Samosas from whole foods (they have wheat but it's a small enough amount to not bother him, miraculously no garlic or onion!) and the Japanese Fried Rice from TJ he also can eat without issue. Both are vegan.