Boil the water in a large cooking pot.
Once the water starts to boil, add the tomatoes, kamias, and onion. Cover and let boil for 8 minutes.
Add the fish (any type) and long green peppers. Cover and cook in medium heat for 10 to 12 minutes.
Add the mustard greens, salt, and pepper. Stir.
Turn the heat off. Cover and let the residual heat cook the leaves for 5 minutes.
Transfer to a serving bowl.
Serve with white rice.
Share and enjoy!