Cook the pasta shells in plenty of boiling, salted water until al dente. Drain, toss in a little sunflower oil and keep warm. Put the remaining oil in a pan with the onion rings and sweat gently until the onion is soft but not browned. Lift out the onion with a slotted spoon and mix with the pasta shells. Put the garlic into the oil in which the onions were cooked and fry, stirring for 1 minute. Mix the cooked garlic into the pasta. Toss the pasta in a warmed serving bowl or dish and sprinkle over the poppy seeds and seasoning to taste. Just before serving, throw in the rose petals.