Bring potatoes and water to cover to a boil in a medium saucepan. Cook 10 to 15 minutes or just until tender. Drain, cool, and cut into 1/2-inch-thick slices.
Stir together olive oil and garlic. Brush half of mixture over both sides of potato slices. Sprinkle potatoes evenly with 1/4 tsp. salt and 1/4 tsp. pepper, and set aside. Brush both sides of steak with remaining half of olive oil mixture; sprinkle evenly with remaining 1/4 tsp. salt and 1/4 tsp. pepper.
Grill steak, covered with grill lid, over medium-high heat (350° to 400°) 6 to 7 minutes on each side or to desired degree of doneness. Cover loosely with aluminum foil, and let stand 10 minutes.
Grill potato slices, covered with grill lid, over medium-high heat 3 to 4 minutes on each side or until browned.
Cut steak diagonally across the grain into thin strips. Serve with potatoes and Red Onion Relish.
this is an unpublished recipe, but she is a cookbook author