For the tuna: Whisk together the mirin, ginger and soy until combined. Add the tuna, toss well to coat, and marinate in the refrigerator for 1 hour.
For the wasabi vinaigrette: Whisk together the soy sauce, wasabi paste and lemon juice in a small bowl until smooth. Add the oil in a slow, steady stream while whisking constantly until combined. Season with the sugar, salt and white pepper and stir well.
For the salad: Remove the tuna from the marinade, shake off the excess and sprinkle the five-spice powder and sea salt equally over all sides. Heat a cast-iron skillet or flat griddle over high heat. Add the oil and heat until rippling, and then sear the tuna in the hot pan, 1 minute per side. Let the tuna rest for 5 minutes before slicing thinly across the grain.
To serve, divide the green beans, mixed greens, tomatoes, Tea-Marbled Quail Eggs and Romaine 2 plates. Fan the tuna slices over the top, scatter the capers and olives over the salads and drizzle the dressing evenly over each plate.
Tea-Marbled Quail Eggs:
Put the quail eggs in a small saucepan and cover with 2 cups of cold water. Add the five-spice, dark soy, light soy, sugar, star anise and tea bags and heat over high heat until the water begins to bubble. Remove from the heat, cover and let stand for 5 minutes. Lift the eggs, a few at a time, out of the liquid with a slotted spoon and crack them all over with the back of a teaspoon, leaving the shells on. Return the eggs to the liquid and let stand until cooled. Chill the eggs in their liquid in the refrigerator for at least 1 hour, preferably overnight. Peel the eggs and rinse briefly just before serving.