Heat the olive oil in a large skillet over medium-high heat.
Season the chicken breasts with salt, pepper, thyme, and paprika on both sides.
Add the chicken to the skillet and cook for about 6-7 minutes on each side, or until golden brown and cooked through. Remove the chicken from the skillet and set aside.
In the same skillet, add the chopped onion and garlic. Cook for about 2-3 minutes until the onion is translucent.
Pour in the chicken broth, scraping the bottom of the skillet with a wooden spoon to deglaze. Let it simmer for about 3-4 minutes.
Lower the heat and add the heavy cream, stirring to combine. Add the spinach if using, and allow it to wilt in the sauce.
Return the chicken to the skillet and pour the sauce over it. Allow everything to simmer for about 5 minutes, ensuring the chicken is well-coated and heated through.
If desired, sprinkle Parmesan cheese on top before serving for added creaminess.