Bring a large pot of water to a boil, salt it, add the pasta and cook until al dente. Drain, reserving 1 cup pasta cooking water.
While the pasta is working, in a large skillet, heat the EVOO over medium-high heat. Add the pancetta and cook until browned, about 5 minutes. Add the onion and cook until softened, 6 to 7 minutes. Add the garlic and cook until softened, 2 to 3 minutes. Stir in the wine, then add the peas and heat through for 2 minutes; season with the thyme, lemon peel and pepper.
Add the reserved 1 cup pasta cooking water and the drained pasta; toss to combine. Add the pecorino-romano and toss. Serve in bowls and top with the ricotta, for stirring in as you eat.