Chop the garlic and chili pepper and brown in a non-stick pan with extra virgin olive oil. Meanwhile, dice the fresh red tuna steaks. Add them to the pan and gently stir for about a minute. Remove from the pan, set aside on a plate, and cover. Now add the capers (previously rinsed in cold water), pitted olives, and tomato purée to the cooking juices, season with salt, and cook for 5 minutes. Add the tuna and cook for about 3 more minutes, then drain the spaghetti al dente into the saucepan and stir gently to coat. Serve, garnishing the dish with a handful of chopped parsley, a few fresh capers, and a couple of green olives.