Cut the tuna into 1/4 inch dice and place it in amedium bowl. In a small bowl, combine the olive oil, lime zest, lime juice, wasabi, soy sauce, tabasco, salt and pepper. Pour over the tuna, add the scallions and jalapeno, and mix well. Cut the avocado in half, remove the seed, and peepl. Cut the avocadeo into 1/4 inch dice. Carefully mix the avocado into the tuna mixture. Add the toasted sesame seeds if using and season to taste. Allow the mixture to sit in the frefrigerator for at least an hour for the flavors to blend. Serve on crackers or toasted baguettes.