Combine olive oil, grated gingerroot, chopped red chilies, and chopped lemongrass in a large bowl.

Add tuna steaks to the marinade, cover, and refrigerate for at least 30 minutes.

Drain the tuna, reserving the marinade.

Grill the tuna steaks for 3-4 minutes per side, or cook under a preheated grill about 4 inches from the heat.

To make the Wasabi Drizzle: Combine white wine, brown sugar, and cider vinegar in a saucepan.

Heat until the liquid comes to a boil, then reduce heat and simmer uncovered until reduced by half.

Cool slightly, then stir in wasabi and sour cream.

To make the Kumara Ginger Fritters: Heat olive oil in a pan, add chopped onion, coarsely grated zucchini, and grated ginger.

Cook until the onion softens, then stir in sweet chili sauce.

Combine the onion mixture, coarsely grated kumara, chopped coriander, lightly beaten eggs, flour, and sesame seeds in a large bowl.

Heat oil for deep frying, add the mixture in 1 tablespoon portions to the oil, and cook until browned on both sides and cooked through.

Drain on absorbent paper.

To make the Chili Coriander Yogurt: Combine plain yogurt, chopped coriander, and sweet chili sauce in a bowl and mix well.

To Serve: Place tuna on a plate and drizzle with wasabi sauce.

Arrange salad greens on the plate, top with kumara ginger fritters, and dollop yogurt on top of each fritter.