One of my best friends worked at Kamameshi restaurant in South San Francisco during one of our summers in high school. When I'd pick her up after the lunch shift, she would graciously share her lunch allowance with me, and we'd have awesome meals at the Kamameshi sushi bar. One afternoon she ordered spicy tuna handroll. Nelson, the sushi chef, had run out of spicy tuna filling. When he whipped up a small batch just for us, I peeked over the sushi bar and took note of what went into it. Since I didn't really know where to buy fresh tuna back then, I never made this recipe until well after college. This amazingly simple combination of ingredients makes for the best spicy tuna handroll I've ever had.