Combine 2 tablespoons olive oil, cumin, fennel seeds, garlic, thyme leaves, and lime zest; season, to taste, with pepper. Rub the marinade all over the tuna steaks. Cover and marinate in the refrigerator.
Heat 2 tablespoons olive oil in a large skillet over medium heat. Add the onions, fennel, a pinch of cumin, and a pinch of fennel seeds and cook, stirring, for 5 minutes (don't let the vegetables brown). Add the zucchini and bell peppers, season to taste with salt and pepper, and continue to cook for 5 minutes.
Separately, heat the remaining 1 tablespoon of olive oil in a small skillet over medium heat. Add the fava beans and cook, stirring, for 1 minute. Add the cherry tomatoes, orange segments, lemon zest and segments, half of the basil leaves, olives, and pistachios.
While the vegetables are cooking, heat a grill pan over high heat. Brush the pan with vegetable oil and grill the tuna steaks for 4 minutes on each side for medium rare. Let rest for 5 minutes before cutting each steak into 4 slices.
Divide the vegetables among 4 warm dinner plates. For each plate, top with the remaining basil leaves and put 2 slices of tuna on top of the vegetables. Season the tuna with fleur de sel and spoon the citrus-fava mixture around the plate. Serve immediately.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Daniel Boulud, 2006