Butter, for grilling
2 teaspoons dry mustard powder
1 1/2 teaspoons dried oregano
1 teaspoon chili powder
3/4 teaspoon salt
1/2 teaspoon freshly ground black pepper
2 (16-ounce) bone-in shell steaks, about 1 1/2-inches thick
1 clove garlic, halved
2 tablespoons olive oil
1 medium onion, sliced
1 bulb fennel, sliced
1 red bell pepper, sliced
Salt and freshly ground black pepper
2 tablespoons chiffonade basil