In a large skillet, drizzle the olive oil over medium heat.
Season the chicken thighs on each side with salt and pepper.
Once thoroughly heated, add the chicken thighs in a single layer. You may have to do this in batches.
Once golden brown, flip the chicken and cook the other side until golden. Remove to a plate and allow to rest for about 5-10 minutes before cutting into thin slices.
Meanwhile, bring a large pot of salted water to a boil.
Add the pasta and cook until barely tender, al dente. Remove and set aside 1/2 cup (120 milliliters) of the cooking water before draining.
Place the large skillet back over medium heat and add another splash of olive oil if needed.
Add the onions and cook, stirring occasionally, until softened.
Stir in the garlic and cook until just fragrant, 30 seconds to 1 minute.
Pour in the reserved 1/2 cup (120 milliliters) pasta water, scraping the bottom of the pan with a wooden spoon to remove any browned bits.
Pour in the chicken stock and bring to a simmer.
Add the sliced chicken thighs and continue to cook until heated through and the liquid has reduced by half.
Toss in the cooked pasta and the heavy cream. Once heated through, stir in the lemon zest and juice. Adjust flavors to taste, adding more salt and pepper as needed.
Remove from heat. Once the mixture has stopped simmering, stir in the freshly grated Parmesan until well coated.
Serve immediately with parsley for garnish and an additional sprinkling of Parmesan if desired.