While the cauliflower and pasta are cooking, make the pesto. Put the spinach, ricotta, walnuts, lemon juice, garlic, salt, and pepper into a blender
or food processor
. Pulse a few times until the ingredients are finely diced and incorporated. Then, with the blade running, slowly add the olive oil until the pesto comes together. Add less for a chunkier consistency, more for a smoother version.