Start by quick pickling the red onions. Add the thinly sliced onions to a mason jar. Fill the jar 2/3 high with vinegar and top the rest with filtered water. Screw on the lid, give it a shake, and let them sit. I always have these on hand to add extra flavor to many dishes.
Next, make the spicy hoisin mayo. Add the mayo, hoisin, and sriracha to a bowl and combine well. Add to a ziplock bag and trim the end to create a perfect drizzle. Set this aside.
Next, I make the tuna filling: add the drained tuna broken up with a fork to a bowl and add the soy sauce, hoisin, sriracha, and mayo. Combine well.
Prep your garnishes: peel the carrots, rough chop the cashews, slice the scallions, and slice the basil. Cut the iceberg lettuce in half, starting from the innermost leaf, and start peeling them out gently until you have 6-8 boats.
Now assemble the cups: Start with a lettuce boat, add a little more than a tbsp of rice, top it with a heaping amount of tuna (about ¼ cups), and repeat until all the boats are filled.
Once they are all assembled on a plate, start garnishing them with all the different accompaniments: carrots, cashews, pickled red onions, scallions, a drizzle of the spicy hoisin mayo, and lastly, the fresh herbs!
There might be some leftover tuna, but just store it in the fridge and have it as a snack!