Stir together the vegan mayonnaise, sriracha, lime juice and soy sauce in a medium bowl. Add the drained tuna, chopped kimchi and scallion, and mix in thoroughly. Allow to sit in the refrigerator for at least 10 minutes. Divide the tuna salad onto two pieces of toasted sandwich bread. Top with avocado slices, cilantro, and the second piece of bread. Enjoy immediately!