If you have super thick chicken breasts, place them between two pieces of plastic wrap and gently pound them down to equal thickness. You do not need your chicken breasts to be thin, however, aim to get each chicken breast even thickness. This will help ensure that the chicken will cook evenly.
Sprinkle each chicken breast with salt, pepper and a pinch of cayenne (optional) for added heat and flavor.
In a large skillet over medium high heat melt the coconut oil. Add the chicken breasts and cook each side for approximately 6-8 minutes depending on thickness. Transfer browned chicken to a clean plate (don't worry if the chicken isn't completely cooked yet, it will be returning to the pan shortly).
To the same skillet add the chopped red onion and reduce heat to medium. Sauté for 2-3 minutes, or just until the onion turns translucent. To the onion add the fresh garlic, ginger and diced chili and stir to combine with the onion. Cook for one minute more.
Add the chicken stock, lime juice and zest, brown sugar and soy sauce. Stir to combine. Bring the mixture to a low boil and reduce to a summer. Allow mixture to simmer for approximately 5 minutes, reducing its liquid. Stir in the fresh chopped cilantro, red chili flakes and coconut milk. Allow mixture to simmer, uncovered, for an additional 5 minutes.
To thicken sauce, whisk together the cornstarch and water in a small bowl and add directly to the simmering coconut broth. Return liquid to a low boil for 2-3 minutes before reducing heat to low.
Add the chicken back to the skillet and cover with a tight lid. Cook for an additional 5-10 minutes, or until chicken is fully cooked.
Serve with rice or noodles, chopped cilantro, red chilis, and fresh lime juice.