Cook sushi rice as instructed in the package. While the rice cooks, chop the tuna steak in 1/2 inch pieces. Place in a bowl and add the soy sauce, sesame oil, 1 tsp sesame seeds, green onions (reserving 2 tbsp to add once you’ve plated the bowls) and chili flakes. Set aside in the fridge.
Place the sliced onion and cucumber in 2 separate bowls, add 2 tbsp of rice vinegar to each bowl plus 2 tbsp of water and set aside.
Once the rice is cooked, place in 3 bowls, top each bowl with marinated tuna, a few avocado slices, onions and cucumbers. Sprinkle the rest of the sesame seeds and green onions, add 1 tbsp of pickled ginger per bowl, and if desired, ad chopped fresh cilantro.