1) For the steaks: in a small bowl, stir together the mustard powder, oregano, chili powder, salt and pepper; set aside. Rub each of the steaks with the cut sides of the garlic halves, pressing the garlic hard into the bone to get the garlic juices flowing. Pat both sides of the steak with the spice mixture.
2) Preheat cast-iron griddle with butter over medium heat.
3) Grill the steaks for 6 to 7 minutes per side for medium-rare. Transfer steaks to a cutting board, tent with foil, and let stand for 5 minutes before serving.
4) For the saute: add oil to a medium sized saute pan over medium heat. Add onions, fennel and red bell pepper and saute until tender. Season with salt, pepper and stir in the basil before serving with steaks.