Place all ingredients except steak cubes into a small bowl, whisk to combine, set aside.
Place steak cubes in an 8 x 8 glass baking dish, then add marinade and toss to coat. Cover baking dish with plastic wrap and marinate steak cubes for at least 2 hours or up to 24 hours in refrigerator.
Preheat grill, charcoal or gas, to medium-high heat. Thread steak cubes onto soaked bamboo skewers. Grill steak kebabs on a clean, oiled grate for about 3 to 4 minutes per side.
Transfer kebabs to a platter. Serve on lettuce leaves with thinly sliced radicchio and green onions and a sprinkle of sesame seeds. Coconut aminos with a sprinkle of red pepper flakes can be used as a dipping sauce.