Slice the cucumbers into 1 inch rounds. Using a small spoon, gently scoop out the seeds, leaving a "bottom" in each piece of cucumber to hold the filling. Turn the cucumber cups upside down on paper towels to drain for about 20 minutes. Pat the inside of the cucumbers dry with clean, dry paper towels. Combine the tuna, lime juice, green onions, and wasabi in a small bowl; mix well and season with black pepper. Just before filling the cucumbers, add the pine nuts and sesame seeds to the fish mixture; mix well. Carefully spoon some filling into each cucumber piece, making a dome of filling on the top of each piece. Serve chilled.