To prepare the walnuts, combine all the ingredients in a small mixing bowl. Heat a large skillet over low heat and cook, stirring often, until the sugar melts and coats the nuts. Transfer to a cookie sheet and bake at 325°, stirring several times, until the walnuts are crisp, about 25 - 30 minutes.
Whisk together the garlic, honey, lime juice, vinegar, and oil. Season with salt and pepper and set aside.
Cut the lettuce into bite-size pieces and chill thoroughly.
Brush the tuna steaks with olive oil, season with salt and pepper. Coat with sesame seeds and sear in a hot nonstick or cast iron skillet. Cook about 2 - 2-1/2 minutes on each side. Keep the tuna warm in a 300° oven while assembling the salads.
Toss lettuce and walnuts together with the vinaigrette. Mound on two dinner plates. Arrange tomato wedges around the edge of each plate. Cut the tuna into bite-size pieces and place in the center.