Cut your tuna fish into chunks and season with salt/pepper. In a bowl mix the cornstarch and 1 egg together into a thick batter.
Coat the fish chunks and leave to rest for 10 mins. In a pan heat some vegetable oil and then shallow until golden brown.
Remove and strain on a paper towel while you make your sauce.
In another pan ,add 2 tsp of oil and the ginger paste. Add your onions,mushrooms,mixed bell peppers, corn and pineapples and stir fry on low heat.
Next pour in the sauce to the mix and give it a good stir. Simmer for 10 mins then add the fish chunks. Add water accordingly,salt/pepper accordingly and leave to cook for 10 mins more.
Remove and serve with chopped red chillies on top if you like it hot. Else serve over plain fried rice or even white rice with a sprinkle of sesame seeds for extra crunch.
Note: You will know when it is ready to serve when the sauce has thicken almost forming a glaze over the fish.