It would not be wrong to call this dish a salad; it does involve a pile of fresh greens, after all. But that descriptor doesn't let on to how hearty, warm and satisfying a plate this is.
The tuna itself, with its deep red color and meaty texture, gives the dish real substance. Sprinkling the fillets with a coating of cracked peppercorns and salt, just as you might a cut of beef, accentuates their steak-like appeal.
Once the fish is seared (which takes mere minutes), the same skillet is used to simmer a lemon and white wine sauce that is enhanced with sautéed garlic, an umami-rich punch of anchovy paste and briny capers. A little butter melted in at the end goes a long way to enrich the sauce, giving it silky body and tempering the tang of the lemon without upsetting the dish's healthful balance.
The sauce, which I suppose you could think of as a warm dressing, is served drizzled over the sliced tuna that is fanned out over a bed of fresh arugula. Whether you ultimately call it a salad, or not, I know you will find it deliciously fulfilling.