In a cast iron skillet, heat up coconut oil. Put chicken thighs in the warm skillet, and flip after 3-4 minutes. Cook another 4 minutes on the other side, and let them get browned on either side. Remove chicken into a bowl and set aside.
Keep the brown bits in the bottom of the skillet - add in the thinly sliced onions. Stir until translucent, about 2-3 minutes.
Add in the garlic, cardamom, and salt. Stir until fragrant, about 1-2 minutes.
Add in the coconut milk can and the tomato paste can. Let them combine and break up the brown bits from the bottom with a wooden spoon.
Add the chicken thighs back in, and cover them with the sauce.
Let this simmer for 20-30 minutes on low heat. Shred the chicken before serving.
Serve over basmati rice (or cauliflower rice if you want to skip the carbs).