It is important to pat your tuna fillet dry with a paper towel. With a sharp knife, dice the tuna into 1 inch pieces. In a medium bowl, mix together the ginger, garlic, soy sauce, lime juice, scallions, sesame oil, Sriracha sauce and sesame seeds. Add the tuna to this mixture and careful toss so all the tuna is coated. Set aside. In another medium bowl, add the avocado with the other lime juice, scallions & oil. Carefully mix. To assemble, use a mold or a ramekin. Use your judgement on size, but aim for something about 3 inch diameter. Whatever you use, you need to oil the inside so everything slips out well when you plate it. I use a mold/ring, so the top & bottom are open. Place the ring on the plate. Start with about an inch layer of your rice. Then add about 1/4 cup of the tuna. Press down with the back of a spoon to make everything even. On top of that a layer of the avocado. At this point I remove the mold/ring. Then, I add a generous spoonful of seaweed salad and sprinkle with a few more seasame seeds for garnish. This is always a crowd pleaser because it is 1) delicious 2) beautiful!! 3) I promise it's so easy. If you don't have the molds, get some. You will use them again. I bought mine on Amazon.