Bring a pot of lightly salted water up to a boil. Add the pasta and cook according to the package directions (boil for 7-10 minutes or until al dente). Remove one cup of peas from the freezer so they can begin to thaw.
While the pasta is boiling, begin to make the sauce. In a large bowl, combine the ricotta, butter, salt (about 1/2 tsp), freshly ground pepper (about 20 cranks of a pepper mill) and the juice and zest of one lemon. When the pasta is almost finished boiling, take 1/3 cup of the hot, starchy pasta water and whisk it into the other ingredients to create a smooth sauce. Adjust the salt and pepper as needed.
Place the peas in a colander and pour the boiling pasta over them to drain (this speeds up the thawing process). When the pasta has drained and is still hot, stir the pasta and peas into the ricotta cheese sauce. Serve hot or cold.