Preheat oven to 425 degrees. Line a large baking sheet with parchment.
In a bowl, stir together the tuna, soy sauce, sesame oil, lime juice, ginger, sesame seeds, and green onions. Let sit while you prepare the tostada shells.
Lightly spray both sides of the yellow corn tortillas and set onto the baking sheet. Bake 7-8 minutes until crispy. Keep an eye on them! They burn quickly.
Place a few avocado slices on each tostada shell. Top with about 1/4 cup of the tuna. Serve with extra green onions and sesame seeds, as desired.