In a large bowl, combine warm water and yeast. Let stand for 10 minutes until yeast dissolves.

Mix in olive oil and salt.

Add 2 cups of bread flour and stir until dough forms.

Knead in the bowl, adding more flour if sticky, for about 6 minutes until smooth and elastic.

Transfer dough to an oiled bowl, turning to coat. Cover with plastic wrap and a towel.

Let rise in a warm, draft-free area for about 1 1/2 hours, until doubled in volume.

Combine soy sauce, olive oil, and wasabi in a medium bowl. Whisk until blended.

Whisk in minced fresh ginger. Season to taste with pepper.

Preheat oven to 400F with a heavy baking sheet on the rack.

Gently knead the dough to deflate. Divide into 4 equal pieces and shape each into a disk.

Place on a lightly floured surface, cover with a towel, and let rest for 15 minutes.

Roll out each piece to a 6-inch diameter round.

Cover the dough rounds again and let rest for 10 minutes.

Roll out 2 dough rounds to 8-inch diameter rounds.

Brush each generously with wasabi sauce.

Sprinkle the heated baking sheet lightly with flour. Transfer dough rounds to the sheet.

Bake crusts until golden and crisp, about 10 minutes. Transfer to plates.

Repeat with remaining 2 dough rounds.

Brush tuna steak with olive oil and season with salt and pepper.

Heat a heavy, large nonstick skillet over high heat. Add tuna.

Sear until brown outside but still pink inside, about 5 minutes per side.

Transfer tuna to a work surface. Slice thinly.

Arrange 1/4 of the tuna on each pizza crust.

Drizzle each with 1 tablespoon of wasabi sauce and sprinkle with chopped green onions.

Serve, passing remaining wasabi sauce separately.