Heat a large skillet over high heat. Season the steak with ¼ teaspoon each salt and black pepper. Cook 4 to 5 minutes per side for medium-rare. Let rest at least 5 minutes before slicing.
Meanwhile, in a large bowl, whisk together the lime zest and juice, honey, ginger, soy sauce, oil, and ¼ teaspoon salt. Add the lettuce, mango, bell pepper, basil, and scallions and toss to combine. Gently fold in the steak and sprinkle with the sesame seeds.