Season the tilapia with salt. Set aside.
In a bowl separate the pineapple from the syrup. Mix the syrup with ketchup, soy sauce, vinegar, sugar, salt, and pepper.
In a pan with hot oil. Fry the fish until golden brown. Flip as needed. Cook in batches then set aside.
In another pan, heat some oil. Saute ginger before sauteing in garlic until aromatic, then onions until slightly soft. Mix in carrots for a few seconds.
Then mix in bell peppers and pineapple tidbits. Saute for a few seconds. Pour in the sweet and sour sauce. Give it a good mix. Bring to a boil.
Pour in the slurry and mix well. Add back the fried fish. Flip and baste to help it absorb the flavors better. Garnish with green onions before serving.