Preheat an indoor or outdoor grill.
In a small bowl, whisk together the soy sauce, Splenda Brown Sugar, hot sauce (optional) and black pepper. Set aside.
Spray the indoor grill with cooking spray. Or, if using an outdoor grill ensure the grates are cleaned and lightly oiled.
Brush tuna and asparagus with the soy sauce marinade. Place onto grill. Grill the tuna for 3 minutes on each side. Grill asparagus, turning often, until beginning to soften (about 6-8 minutes). Remove tuna and asparagus from grill, sprinkle with sesame seeds and set aside to cool. Tuna should be slightly pink in the center but not raw.
Toss the lettuce, red bell pepper and cucumber in a salad bowl.
In a small bowl whisk dressing ingredients. Pour over salad and toss gently to coat. Divide the salad equally among four plates.
Once tuna and asparagus are cool to room temperature or slightly warmer, slice the tuna and divide equally among the four salads (just under 4 ounces of tuna per salad). Lay it gently on top of the salad.
Cut the asparagus spears in half and lay them around the edge of the salad.Serves 4