To pickle the cucumber, chop it finely (removing the seeds in the middle if you wish). Then put it in a bowl with 1tsp salt and the rice vinegar. Let it rest for 15 minutes, stirring occasionally
Boil the eggs for 10 minutes and drop them in an ice bath (optional) to ensure they're perfectly cooked. In a bowl, combine the eggs, tuna, salt and pepper (to taste), pickled cucumber (drained), mayo and dill. Mix thoroughly
Open the baguette and spread the mixture (don't be shy with the filling). Optionally you can add some chili flakes or hot sauce if you're feeling spicy. Buon appetito!