Heat coconut oil in a large skillet over medium heat until shimmering. Add the chopped onion and sauté until translucent and fragrant, about 5 minutes.
Add the minced garlic and grated ginger to the onions; cook until the mixture becomes aromatic, about 1 minute, stirring constantly to prevent burning.
Sprinkle the curry powder over the onion mixture, stirring well to coat everything evenly. Cook for 1-2 minutes until the spices toast slightly and release their aroma.
Add the chicken chunks, stirring to coat them with the spiced mixture. Cook until the chicken is browned on all sides, about 6-8 minutes.
Pour in the coconut milk, stirring gently as it melds with the spices and chicken. Bring the mixture to a gentle simmer.
Squeeze in the lime juice, add a pinch of lime zest, and splash in fish sauce if using. Stir to combine and taste; add salt and pepper as needed.
Reduce the heat to low and let the curry simmer uncovered for about 15 minutes, or until the chicken is cooked through and the sauce has thickened slightly.
Add the fresh spinach and cook just until wilted, about 2 minutes, stirring gently to incorporate color and nutrients.
Taste the curry and adjust seasoning with lime, salt, or chili flakes if you prefer more spice or brightness.
Serve the vibrant chicken coconut curry hot, garnished with additional lime zest or herbs if desired, alongside steamed rice or warm naan for a complete meal.
