Gather the curry ingredients, as well as the curry sauce.
Pour the sauce into a wok or large frying pan and set over medium-high heat. If using makrut lime leaves, add them now. Bring the sauce to a gentle boil.
Add the mushrooms and green beans and stir well. Reduce the heat to medium and bring the sauce to a simmer. Cover and cook for 6 to 8 minutes or until the vegetables have softened.
Gently stir in the fish and tomato. Cover and continue simmering for another 2 to 3 minutes or until the fish is flaking and cooked to your liking.
Do a taste test for flavor, adding more fish sauce if not flavorful or salty enough. If too sour, add a little more sugar; if too salty or sweet, add the fresh lime juice or lemon juice.
Spoon the curry into a serving bowl or serve straight from the pan. Sprinkle with coriander and garnish with lime or lemon wedges if desired. Serve with Thai jasmine rice and enjoy.