This dish is like the love child of raw sushi and cooked fare. The flavors are so reminiscent of sushi, but with the substance and feeling of a regular entree. Be careful of the quantity of wasabi used - this will clear out your sinuses big time!
In a small bowl, whisk together wasabi paste, garlic, ginger, vinegar, soy sauce, sesame oil, and salt until smooth. Slowly drizzle in the canola oil while whisking. Set the vinaigrette aside until ready to serve.
Mix all the spices together. If using a star anise, whole coriander or whole mustard seed, grind to a fine powder using a clean coffee grinder or a mortar and pestle. Sift through a fine sieve to remove coriander husks if using whole coriander.
Using a mandoline or vegetable peeler, cut the cucumbers lengthwise into long, paper-thin ribbons. Continue to slice each cucumber lengthwise until you reach the seeds, then turn the cucumber and slice again.
Season the tuna fillets with a little salt and then dredge them in the spice mix. Place the tuna in a preheated saute pan or skillet with a little olive oil and cook 2 minutes on each side over medium-high heat.
To serve, toss the cucumber ribbons in a large bowl. Pour half of the vinaigrette on top and toss until well coated. Drizzle the remainder of the vinaigrette onto each of 8 plates. Arrange a pile of cucumber salad on each plate, and then top with a portion of tuna.