I have never encountered a sushi shop not happy to sell me 8 ounces of tuna. Add "fried" capers if you like--instead of frying, microwave them on high for 1 to 2 minutes until they are crispy.

Simmer, stirring occasionally, until juices thicken slightly, 15-20 minutes. Stir tuna, capers and lemon zest into the sauce. Add drained spaghetti and a generous drizzle of olive oil, and toss ...