Soak 8 bamboo skewers in water. In a medium bowl, whisk together the soy sauce, oil, five-spice powder and allspice. Stir in the hot sauce. Add the steak and toss to coat; refrigerate.
Bring a saucepan of lightly salted water to a boil. Add the sweet potatoes, lower the heat and simmer until just fork-tender, about 8 minutes; drain and let stand until cool enough to handle.
Meanwhile, using a food processor fitted with a shredding disk, shred the radishes and transfer to a bowl with the pineapple. Toss and season with salt.
Preheat the broiler. Thread the meat and sweet potato onto the skewers and arrange on a broiler pan; brush the sweet potatoes lightly with oil. Broil the kebabs for about 6 minutes, turning once, for medium-rare. Serve with the slaw.