Season the chicken with salt and pepper. In a large pot over medium-high heat, melt some butter and add the chicken pieces. Cook until browned and fully cooked through, about 6–8 minutes. Remove from the pot and set aside.
In the same pot, melt more butter if needed, then add the minced garlic. Sauté until fragrant, about 30 seconds. Add crushed red pepper flakes and stir.
Pour in the chicken broth while scraping up any bits stuck to the bottom of the pot. Stir in the heavy cream and bring to a gentle simmer.
Add the fresh tortellini into the simmering sauce and cook for about 4–6 minutes until tender and heated through.
Return the cooked chicken back into the pot along with grated Parmesan cheese. Stir until melted and well combined. Let cook for another couple of minutes before serving.