1/4 cup olive oily plus oil for grilling
1 onion, peeled and coarsely chopped
1 lemony thinly sliced and seeded
Juice of 1 lemon
1 cup chicken stock
1 pound trenne pasta
2 tablespoons capers, drained
1/4 cup minced fresh flat-leaf parsley
Sea salt and freshly ground black pepper
4 tuna steaks, 6 ounces each
Preheat a grill or broiler.
In a large skillet over medium heat, heat the olive oil and saute the onion until softened, but not browned, about 3 to 4 minutes. Add the lemon slices and cook until softened, about 2 to 3 minutes. Deglaze the pan with the lemon juice. Reduce heat to a simmer and add the chicken stock. Continue to cook, uncovered, over low heat for 10 minutes, until slightly reduced.
In a large pot of salted boiling water, cook the pasta according to package directions, until al dente. Toss with the onion-lemon mixture; add the capers, parsley, and salt and pepper to taste. Keep warm.
Brush the tuna with olive oil and season with salt and pepper. Grill or broil for 4 to 5 minutes on each side, or until lightly browned on the outside, but still rare on the inside. Serve the pasta topped with a piece of grilled tuna.