Salt and pepper your tilapia fillets. Coat them with the cornstarch and set aside.
In a pan over medium high heat, add enough oil to coat the bottom of the pan to shallow fry.
Once hot, fry your tilapia 3 minutes per side until golden yellow. Remove and set aside.
In the same pan over medium high heat, add your shallots and sauté for 1 minute. Add your garlic and sauté for 30 seconds.
Add your tomatoes and sauté for another minute. Add your pickled mustard greens and cook for another minute.
Add back your 3 fried tilapia fillets and 1.5 cups of water. Season with 1.5 tablespoon fish sauce and ½ teaspoon sugar.
Gently combine so the fish is mixed well with the vegetables and sauce.
Reduce the heat and simmer for 20 minutes.
Serve hot with rice.
