This easy lemon chicken pasta combines tender chicken, spaghetti, and spinach with a bright, creamy ricotta sauce. Fresh lemon, garlic, oregano, and a pinch of red pepper flakes add bold flavor without heavy cream.
Make the lemon ricotta. In a small bowl, stir together the ricotta, the zest of the small lemon, 2 tablespoons of its juice, salt, black pepper, and red pepper flakes, if using. Set aside.
Start the pasta. Bring a large pot of salted water to a boil over high heat. Add 8 ounces of spaghetti and cook according to the package directions while you prepare the chicken.
Prepare the chicken and aromatics. Set a large, high-sided skillet over medium heat and add the olive oil. Slice each chicken breast horizontally into two thinner cutlets. Once the oil begins to shimmer, add the onion and garlic.
Season and cook the chicken. Season the chicken all over with salt, black pepper, and oregano. Add it to the skillet and cook for 5 minutes. If the onions begin to brown too quickly, add 1/4 cup of pasta water and scrape up the browned bits. Flip the chicken, then add the zest of the remaining lemon and 2 tablespoons of its juice. Cook for another 5 minutes, or until the chicken reaches 160°F. Add spoonfuls of pasta water as needed to keep the onion and garlic from burning. Transfer the chicken to a plate and tent it with foil.
Wilt the spinach. Reduce the heat to low. Add the spinach and stir until wilted, about 2 to 3 minutes. If the skillet looks dry, add about 1/4 cup of pasta water.
Make the sauce. Before draining the spaghetti, reserve 1 1/4 cups of pasta water. Add the drained pasta and lemon-ricotta mixture to the skillet and toss to coat. Add 3/4 cup of the reserved pasta water and toss again, adding more as needed to reach your preferred consistency.
Finish and serve. Slice the chicken into strips and return it to the skillet. Toss everything together, divide among pasta bowls, and serve.