Season chicken thighs generously with salt, pepper, and smoked paprika.
Heat avocado oil in a heavy skillet over medium-high heat. Sear chicken, skin-side down, 5–6 minutes until deeply browned. Flip and sear 3 minutes more. Remove and set aside.
Add onions to the same skillet and cook 10 minutes, stirring often, until deeply caramelized.
Add garlic and cook 1 minute, then pour in broth, scraping up browned bits.
Whisk in xanthan gum a little at a time until gravy thickens slightly.
Return chicken to the skillet, skin-side up, spooning gravy over top.
Cover and simmer 20–25 minutes, until chicken is tender and cooked through.
Garnish with parsley and serve.