Bring a large pot of salted water to a boil. Add in the pasta and cook according to the packaging instructions or until al dente.
Five minutes before draining the pasta, add in the kale and cook until softened. Reserve 1 cup of pasta cooking water and drain the pasta.
Put the now-cooked pasta back in the pan.
While the pasta is cooking, make the ricotta lemon pasta sauce by mixing ricotta cheese, parmesan cheese, garlic, lemon zest, lemon juice, and salt and pepper in a bowl.
Add in the ½ cup of reserved pasta sauce and whisk until creamy. Set it aside.
To cook the shrimp: Heat olive oil in a large stainless steel skillet. Cook shrimp 2 minutes on each side. Season with salt and pepper.
To assemble the shrimp ricotta pasta: Add the ricotta sauce to the pasta and toss gently. It should be very creamy as you toss it with the help of the residual heat coming from the freshly cooked pasta. If you need it, add in the remaining pasta liquid and turn the heat on for a minute or so as you toss and turn the pasta.
Add the cooked shrimp and gently incorporate, ensuring that it is evenly distributed.
Taste for seasoning and add in if necessary. Garnish with a sprinkle of shredded parmesan cheese and red pepper flakes, if using. Serve.