1. Preheat grill to medium-high heat.
2. Place onions on a piece of aluminum foil and drizzle with olive oil. Fold the foil so it encloses the onions. Wrap with another piece of foil.
3. When the grill is ready, place the onion packet on the grate over indirect heat. Cook, covered, until the onions are tender, about 20 to 30 minutes. Remove from heat and let cool.
4. While onions cool, cook the steak. Brush the grill with vegetable oil. Season steak with salt and pepper and place on the grill. Cook, covered, until deeply browned on the outside and rare inside, about 5 to 6 minutes per side. Steaks should have an internal temperature of at least 145degreesF. Transfer the steaks to a cutting board and let rest 5 minutes.
5. While the steak cooks, prepare the relish. Drain any juices from the onion packet into a medium bowl, then chop the onions and add them to the bowl. Stir in both kinds of olives, capers, and oregano.
6. To serve, cut steak in four pieces. Garnish each with the Vidalia relish. Serve any remaining relish in a bowl on the side.
Source: fresh magazine May, June 2010