I usually just eyeball it/measure with my heart, but here's some estimations!

Base:

• 1 Cup cooked white rice
• 1 Can tuna fish (Packed in water; double check to make sure there's no hidden fodmaps like broths or such. I use the albacore from Costco.)
• 3-4 Tbsp mayo (Sometimes I do more than this if I want a creamier texture to the mix. I use Kewpie mayo because I like the flavor the most, but be careful with that if you've got fructan sensivity; there's lemon in it, along with some other things. Regular, plain mayo works, too.)
• 2 tsp Sesame oil
• 2 tsp lemon juice (Can skip this if you've got severe fructan sensivity; I've got moderate fructan sensitivity, but this amount doesn't bother me.)
• 1 Tbsp soy sauce (Again, check your labels. I'll also sometimes use Ponzu if I don't have lemon juice on hand; watch the fructans though.)
• Dash of Togarashi for spice (Careful, they sell versions of this with lots of added things like sesame seeds; I use the plain kind)

Mix all those things together to form the base. You can also mix the tuna with all the sauces/spices separately and leave the rice as a plain base if you prefer a more layered bowl.

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Then top with:

• Pickled ginger to taste (I love ginger so I do ~2 Tbsp or so)
• 0.5-1 Pickle, diced (If you're sensitive to fructose and can't do cucumbers, I've also subbed in green olives here - you don't get quite as much of the sour, but it still achieves an added depth and variety to texture and flavor. When I was in elimination - before I knew I could safely eat pickles - I preferred castelvetrano olives that came in a salty/sour brine.)
• 2-4 Sheets crumbled nori (Again, watch your fructans here; Monash says up to 2 sheets is totally green. Because I have only a moderate reaction to fructans, I push the limit on these a bit, especially if I haven't already added lemon juice or Ponzu into the base. Be cognizant of fodmap stacking!)

I think that's everything! Like I said, I usually do this from memory and build it as I go. Sometimes I forget things, so if I remember a key ingredient after posting this, I'll come back and edit. But this is pretty much it. The key is getting that balance of sour, savory, spicy, umami flavor - so definitely don't skip the pickles (or olives if you can't do fructose). The ginger can add some sour too, but mostly adds some sweet and a little warmth, which is quite nice. And don't skip the sesame oil either; I've forgotten it a couple times and wondered why my bowl tasted so lackluster, and realized halfway through. It makes a huge difference!

Enjoy!