Put the ricotta, pesto, tomatoes, green onion in a bowl. Once the pasta is cooking, take a couple tablespoons of the cooking water and put it in the bowl. Stir the ricotta and other ingredients briefly to allow the water to loosen the ricotta. If you feel it needs a bit more loosening add more pasta cooking water 1 tbsp at a time. Do not let it get too watery. You want the ricotta to act as a sauce to coat the pasta.