Start by making the rice beforehand so that you can put the curry together when everything is done.
Gather the green curry paste ingredients together. Slice the lower half of the lemongrass into small slices until the purple rings disappear. Crush the garlic with the back of your knife and de-stem the kaffir lime leaf. Add all the curry paste ingredients together in the food processor and add about ¼ cup water (or enough to help the paste form). Grind until the paste has reached a paste-like consistency.
Cut the carrots, mushrooms, onion, and garlic.
Use cooking spray and spray a skillet, then sauté the curry paste along with the garlic and onions.
Turn the stove to low heat and add in coconut milk. High heat will make the milk evaporate very fast. If that happens, you can deglaze the sauce with water.
Add the vegetables and cook until they soften, about 3-5 minutes.
Add the cod pieces in a single layer and cook for 1-2 minutes each side, or until cooked thoroughly.
Season the curry sauce with fish sauce and sugar. Taste and adjust if needed.
Garnish with cilantro and chili flakes if desired and serve with rice, and enjoy your delicious green fish curry recipe.