by Tami Gilliam, s/v Heart of Gold
In a small bowl, whisk the vinegar, soy sauce, mustard, oil, ginger, and garlic. Using about 2 tbsp of this vinaigrette, brush the entire surface of the tuna steaks. Toss the remaining vinaigrette with the arugula.
Heat a large nonstick skillet over medium-high heat. Sprinkle the tuna with salt. Pour the sesame seeds on a plate and dip each tuna steak into the seeds to coat all sides. Lightly coat steaks with cooking spray and cook for 2 minutes per side or until medium-rare. (Reduce the heat to medium if the seeds begin to burn).
Place equal portions of arugula onto each of 4 plates and top each with a tuna steak.
*Several people asked what arugula was:
Arugula is a spicy little leaf, which some describe as bitter and others characterize as having a "peppery-mustardy" flavor. Because it is so potent on its own, it is often mixed with milder greens to produce a nice balanced salad. It can also be sautéed in olive oil. You can substitute most any green for arugula, but the closest matches are Belgian endive, escarole, and dandelion greens.
I generally find arugula in a package in the organics section at my grocery. If you can't find it, I would substitute spinach.