Sushi rice: Wash and rinse the rice until the water runs clear. Drain well. Cook according to package instructions. Once done, season with rice wine vinegar and cover with a damp cloth to prevent drying.
California roll – prepare the fillings: Mix the imitation crab meat with mayonnaise. Cut cucumber and avocado into thin strips. Squeeze lemon juice over avocado to prevent browning.
California roll – roll the sushi: Cover a bamboo sushi mat with plastic wrap. Place a sheet of nori, shiny side down, on the mat. Wet your fingers and spread the sushi rice evenly over the nori. Arrange crab mixture, cucumber, and avocado along the bottom edge. Roll the mat tightly over the filling into a cylinder. Cover rolls with a damp cloth.
Spicy tuna roll – prepare the filling: Combine tuna, sriracha sauce, sesame oil, and scallions in a bowl.
Spicy tuna roll – roll the sushi: Place a sheet of nori on a bamboo mat covered in plastic wrap, shiny side down. Spread sushi rice evenly and sprinkle with sesame seeds. Arrange the tuna mixture along the bottom edge. Roll the mat tightly into a cylinder. Cover with a damp cloth.
Make the spicy mayo: In a bowl, combine mayonnaise, sriracha sauce, and lime juice. Whisk until smooth.
Iced matcha latte: Whisk matcha powder with hot water until smooth and foamy. In a glass, mix water and sugar to desired sweetness. Pour in milk, then the matcha. Stir well. Pour over ice to serve.
Finish and serve the meal: Wet the blade of a sharp knife and cut each spicy tuna roll into 6–8 pieces, cleaning the blade with a damp cloth every few cuts. Top rolls with spicy mayo or serve on the side. Cut each California roll into 8 pieces using the same method. Serve the sushi with optional wasabi, pickled ginger, and soy sauce. Enjoy iced matcha latte.