Cut a pocket into the side of the tuna steaks; set aside.
In a bowl, combine olive tapenade, garlic, and capers. Stuff tuna steaks with olive mixture and secure opening with toothpicks. Place stuffed tuna steaks in a large resealable plastic bag with the salad dressing. Squeeze out air and seal bag. Place in second bag to prevent any leaking. Marinate in refrigerator 1 to 3 hours.
Remove tuna from marinade and let come to room temperature, about 20 minutes. Discard marinade.
Heat an oiled grill pan over medium-high heat. Place tuna in grill pan and cook 3 to 4 minutes per side or until done. Be careful not to cook past medium or tuna will dry out quickly. Remove from grill pan and set aside.
Place salad mix onto a large serving platter. Garnish with slices of boiled egg, green beans, tomato wedges, and sliced potatoes. Remove toothpicks from tuna and place on top of greens.
Recipe courtesy of Sandra Lee, 2008