To a large skillet over high heat, add the olive oil. Then, add the chicken thighs and season with salt and black pepper. Sear the chicken for about 3 minutes on each side until browned. Meanwhile, finely dice the onion, slice the mushrooms, and mince the garlic.
Once the chicken is done, transfer the seared chicken to a plate. To the same skillet, add the mushrooms and saute for 3-5 minutes until golden. Add the diced onions and minced garlic and sauté for about 1 minute until soft and fragrant.
Then, add the sundried tomatoes and chicken broth and scrape down the bottom of the pan using a spatula. Reduce the heat to low. Continue stirring until about half of the chicken broth has evaporated.
Add in the heavy cream, red chili flakes, spinach, and seared chicken. Simmer for about 2 minutes, uncovered, until the spinach is bright in color and wilted. Turn the chicken to coat both sides in the creamy sauce evenly.
Serve the chicken on a serving plate topped the creamy sauce and spinach. Garnish with chopped parsley and a wedge of lemon.