Cut fillet into serving size pieces and season with salt and pepper.
To Make Batter:
Mix dry ingredients together and set aside. Whisk egg and add water.
Pour liquid into dry mixture and beat until smooth.
Dip pieces of fish into the batter, then fry in hot oil until golden brown. Drain on absorbent paper.
To Make Lemon Sauce:
Melt margarine in a saucepan. Mix in the cornstarch, sugar and salt.
Gradually stir in the water or milk and cook stirring constantly until mixture thickens.
Remove from flame and stir in the lemon or lime juice and rind.
To Serve: Serve with Lemon Sauce and a baked potato or with boiled rice. Garnish with lemon wedges.