Cut tuna into 1" cubes. Slice brown onion thinly. Slice green onion diagonally. Set aside.
In a medium bowl, mix Soy Sauce, sesame oil, chili sauce, and garlic together.
Add tuna and onions to the bowl and coat with the sauce very well. Refrigerate for 30 minutes or so.
Sprinkle with Furikake.
If making a Poke bowl, put 1 cup of Steamed Rice in a bowl, top with shredded Nori and Tuna.