Peel lemon, lime, and orange. Reserve peels and save fruit for another time. Season tuna with salt and pepper on both sides. Combine with citrus peels, rosemary and olive oil in a Ziploc plastic bag. Marinate overnight.
Preheat oven to 400 degrees F.
Make the dressing. Mix together white wine vinegar, dijon mustard, lemon zest, balsamic vinegar, sugar, and garlic in a medium bowl. Slowly whisk in the olive oil until thickened. Season with salt and pepper.
Cut fingerling potatoes in half. Season the potatoes with salt and pepper and toss with 1 tablespoon oil. Spread the potatoes on a baking sheet and roast for 20-25 minutes or until tender. Remove from the oven and let cool.
Place eggs in a medium pot and cover with water. Bring to a rapid boil over high heat. Turn off the heat and let the eggs sit in the hot water for 8 minutes. Drain and place eggs in an ice bath to stop the cooking process. Peel eggs and cut in half.
Bring a medium pot of salted water to a boil. Add the green beans and blanch for 2-3 minutes or until crisp-tender. Remove from heat, drain and immediately shock in an ice bath until cool.
Remove the tuna from the marinade, discarding the aromatics. Heat 1 tablespoon oil in a skillet or cast iron pan over high heat until hot. Sear the tuna for 2 minutes on each side for medium rare. Remove the tuna from the pan and let rest for 5 minutes. Slice into ½-inch slices.
Toss together mesclun greens with the potatoes, egg, green beans, tomatoes, olives, and capers. Divide onto two plates. Top with seared ahi tuna and drizzle vinaigrette on top. Serve immediately.