Combine orange juice, vinegar, tamari, and ponzu sauce. Gradually whisk in sesame oil until emulsified. Keep refrigerated until ready to use.
In a mixing bowl, just before you are ready to serve, combine tuna, cilantro, black sesame seeds, green onion and tomato dice. Add 4 tablespoons tamari vinaigrette and mix gently. Season with salt and freshly ground white pepper. Taste and adjust seasoning. Add shredded nori and lemon zest and lemon juice. Peel, seed and dice avocado and and gently add to mix.
On individual spoons, place a small amount of tuna tartare. Top with a little tobiko and garnish with daikon sprouts. Serve immediately.