To make the vinaigrette, place the honey in a medium bowl and add the fennel seed, if using. Whisk in the orange and lemon juices. Gradually whisk in the oil. Season with salt and pepper.
Combine the arugula, fennel, oranges, and berries in a large bowl.
Season tuna steaks on both sides with the salt. Pour the cracked black pepper in a shallow dish or on a sheet of waxed paper. Press one side of the tuna into the pepper to coat.
Heat the oil in a large skillet over medium-high heat. Add the tuna, pepper-side down. Cook, turning once, until the tuna is seared on the outside but rare within, about 4 minutes. If you like your tuna more well-done (don’t go past medium doneness!), cover the pan and cook for 2 to 4 minutes longer. Slice each steak against the grain into 1/4-inch slices.
Add the vinaigrette to the arugula and berries; toss well. Sprinkle with the pecans. Heap equal amounts on each of 6 dinner plates or on a large platter. Arrange the tuna slices decoratively around the salad. Serve immediately.