I've had the seared tuna in nice restaurants, but this is better than all of them. One tablespoon of wasabi sounds like a lot of heat, but somehow this cooking method mellows it to almost nothing, just leaves the flavor. Really really great.
Cooking in foil packets makes for a tidy grill, and allows all the flavors to mingle and intensify. Here, thick slices of potato and onion are seasoned and cooked with butter until tender and brimming with flavor.