Heat avocado oil in a large Dutch oven or heavy-bottomed pot over medium heat.
Add onion and cook 4–5 minutes until softened and lightly golden.
Add garlic and ginger and cook 30–60 seconds until fragrant.
Stir in curry powder, turmeric, cumin, coriander, smoked paprika, salt, and pepper. Cook briefly to bloom the spices.
Add chicken pieces and stir to coat in the spices. Cook 3–4 minutes, just until the chicken is opaque on the outside.
Add sweet potatoes, broth and coconut milk. Stir to combine.
Bring to a gentle boil, then reduce to a low simmer. Cover and cook 25–30 minutes, until sweet potatoes are tender and chicken is cooked through.
In a small bowl, whisk arrowroot starch with 2 tablespoons water. Stir into the curry.
Simmer uncovered 5–8 minutes, stirring occasionally, until the curry thickens slightly. If using kale, add in this step.
Turn off the heat and stir in spinach and lime juice. Taste and adjust seasoning as needed.
