Cook the pasta in a large saucepan of lightly salted boiling water for 10–12 minutes, or according to the packet instructions, until al dente.
Meanwhile, scald the tomatoes in a bowl of boiling water for 30 seconds, drain then refresh under cold running water. Peel off the skins, then scoop out the seeds and roughly chop the flesh. Put the flesh in a small saucepan.
Add the diced capsicum, garlic, olive oil, parsley and, if you are using them, the chilli flakes to the pan with the tomatoes. Season to taste. Warm this sauce over a low heat.
Drain the pasta and tip into a heated serving dish. Pour over the warm sauce, toss with the pasta and serve at once, garnished with parsley.