Combine tapioca flour, all purpose flour, garlic salt, and Italian herbs in a small bowl. Dredge chicken thighs through the mixture and shake off excess flour.

Heat olive oil and butter in a large skillet over medium heat. Add chicken thighs and cook until golden brown, about 5 minutes on each side. Remove chicken from skillet.

Wipe out skillet, leaving just a little bit of the fond. Add minced garlic and cook until fragrant, about 1 minute. Pour in tomato sauce, cream, and milk; stir to combine. Season with red pepper flakes and mix in spinach. Allow spinach to wilt, about 3 minutes. Return chicken thighs to the skillet and heat until warmed through. Serve topped with freshly shaved Pecorino Romano cheese.