If it’s the oligosaccharides or fructans that are fucking you up, you can heat (not fry) onions in however much oil you’re okay with in your final dish, and then just remove the onions. The flavor compounds are oil soluble, but the oligosaccharides/fructans aren’t. Smaller pieces = more intense onion flavor.

I don't mind the flavor but I hate that I'm an onion/garlic sweater. For days after eating garlic or most onions, I stink so badly no perfume or deodorant or antiperspirant can control it. As a girl growing up, it was a real problem, and once I was old enough to do my own cooking I started leaving them out, or using sweet onions when they were too important to exclude.

I'm also capsaicin-sensitive, like major ass-bleeding bad, so I minimize spicy peppers and use bell peppers plus black pepper/wasabi/horseradish/ginger for spice. If it's not my cooking I get "Mild" and do the best I can with it.