Score duck skin lightly and season with Cajun seasoning, salt, and pepper.
Heat a heavy skillet over medium-high heat (no added oil needed). Sear duck pieces, skin-side down, 6–7 minutes, until well-rendered and browned. Flip and sear 3 minutes more. Remove and set aside.
Pour off all but 2 tbsp of the rendered duck fat. Add onion and bell pepper, cooking 6–7 minutes until softened.
Add garlic and cook 1 minute, then pour in broth, scraping up browned bits.
Whisk in xanthan gum to lightly thicken.
Return duck to the skillet, cover, and simmer 45–50 minutes, until tender.
Serve smothered in gravy.