Season the chicken: Pat the chicken thighs dry and season both sides with salt and black pepper. This helps them brown evenly in the next step.
Sear the chicken: Heat olive oil in a large pot over medium-high heat. Sear the chicken thighs until golden on both sides, about 4 minutes per side, then remove to a plate.
Sauté garlic and tomatoes: In the same pot, add the garlic and chopped sun-dried tomatoes. Cook, stirring, until fragrant, about 1 minute, scraping up any browned bits.
Add seasoning and broth: Stir in the Italian seasoning and red pepper flakes if using. Pour in the chicken broth and stir well.
Simmer the chicken: Return the seared chicken to the pot. Bring to a simmer, cover, and cook until the chicken shreds easily with a fork, about 15 minutes.
Shred the chicken: Remove the chicken to a cutting board and shred it into bite-sized pieces using two forks. Set aside.
Stir in cream and cheese: Lower the heat and stir in the heavy cream and parmesan cheese. Simmer gently until the broth turns a soft, rosy color and thickens slightly, about 3 minutes.
Return the chicken: Add the shredded chicken back into the pot and stir to combine with the creamy broth.
Cook the gnocchi: Add the gnocchi directly to the simmering soup. Cook just until the gnocchi floats to the top, about 2 to 3 minutes.
Wilt the spinach: Stir in the fresh spinach and cook until just wilted, about 1 minute. Taste and adjust salt as needed.
Serve: Ladle the soup into bowls and garnish with chopped fresh parsley and extra parmesan if desired.