With paper towels, thoroughly dry ahi tuna. Brush with vegetable oil; season with kosher salt and black pepper. Heat a sauté pan until very hot; sear tuna for 1 minute per side. Remove from pan and allow to cool; cut into 30 slices. Thinly slice grape tomatoes to make 30 slices. Thinly slice hard-cooked eggs into 30 slices. Cut ciabatta loaf in half horizontally; cut each half into pieces to yield 30 pieces. Coat squares with mayonnaise; top with tuna, 3 slices of tomato, and a slice of hard-cooked egg. Add a small pinch of olive tapenade.