This is a great question! Birdseye chili can be subbed for Fresno peppers (just use one though!), Thai chilies, habanero pepper (also only one) or serrano peppers if you are in a pinch. You can also use 1/2 teaspoon of red pepper flakes for the easiest sub! Coconut milk can be subbed with heavy cream, but I really prefer the flavor of coconut for this. As for the fish, I have more suggestions in the section above!