Whisk together the miso paste, soy sauce, vinegar, sugar, garlic, ginger and olive oil. Marinate the steak in a glass or non-reactive bowl, or resealable bag, for about 15 minutes.
Heat a grill pan or grill to medium high heat. Grill the steak for about 6 minutes per side, or until a thermometer inserted into the thickest part reads 120°F. Allow the steak to rest while you prepare the rest of the salad.
In a large bowl, toss together the greens, red cabbage, onion, radish, and tomatoes.
In a jar, whisk together the miso paste, garlic, ginger and vinegar. Add the olive oil and sesame oil, season with salt and pepper. Seal the jar with a lid and shake vigorously.
Lightly dress the salad with some of the dressing, then arrange on a platter. Slice the steak against the grain and place on top of the salad. Drizzle with a little more dressing and top with the green onions and sesame seeds. Season to taste with salt and pepper.