Prep the Chicken: Season the diced chicken generously with salt, pepper, and about 1/4 tsp of the turmeric. Heat the large deep skillet or Dutch oven over medium-high heat with the coconut oil until shimmering. Add the chicken pieces in a single layer and sear for 3–4 minutes until lightly browned on all sides. Remove the chicken to a plate and set aside, reserving the pan drippings.

Sauté the Aromatics: Reduce the heat to medium. Add the diced onion and minced jalapeno (if using) to the skillet. Cook gently for about 5 minutes, stirring occasionally, until the onion is soft and translucent. Add the minced garlic and fresh ginger, cooking for 60 seconds until fragrant.

Bloom the Spices: Add the remaining cumin, turmeric, coriander, and cayenne (if using) to the pan. Cook and stir for about 1 minute to release the spices' essential oils.

Build the Sauce: Stir in the diced tomatoes, scraping up any brown bits from the bottom of the pan. Bring to a low simmer. Pour in the full-fat coconut milk and stir until uniform and creamy. Simmer for 2–3 minutes to thicken slightly if desired.

Simmer and Finish: Return the seared chicken and any juices to the skillet. Reduce heat to low, cover, and simmer for 10–12 minutes until chicken is cooked through (internal temperature 165°F).

Brighten and Adjust: Turn off the heat. Stir in the lemon juice. Taste and adjust salt, pepper, or heat. Garnish with fresh cilantro and lime wedges if desired. Serve immediately.