In a medium-sized saucepan, boil water and add salt after it starts boiling. Add your pasta, and cook according to the package instructions to al dente. When the pasta is cooked, reserve 1 cup of the pasta water and drain the pasta.
Meanwhile, in a skillet, heat olive oil on medium heat and saute garlic very lightly without allowing the garlic to brown. About 30 seconds. Add the ricotta cheese, stir to melt the cheese over low heat, then add about a fourth of a cup of the reserved pasta water. Whisk it in.
Add lemon zest and lemon juice, season with salt and pepper, add parmesan, and cook for 1 minute. Add spinach, and cook for 1 more minute for the spinach to wilt.
Add the hot pasta along with about fourth cup of reserved pasta water, and toss it using kitchen tongs until the sauce is emulsified and coats the pasta. Add more pasta water if needed until you reach the desired consistency (if you don’t use up all the pasta water, save some to reheat the pasta later).
Remove from heat, and serve with extra parmesan and lemon zest if desired.