Take the prawns in a large bowl. Add in the flour, cornflour, ginger garlic paste, soy sauce, and egg. Mix well.
Heat oil in a pan. Drop in the prawns one at a time and fry till golden. Remove from oil and place them on a paper towel to drain. Keep them aside.
Now for the sauce, take 2 tbsp of oil in a pan. You can use the oil in which you fried the prawns.
Add in the chopped garlic and chopped ginger. Saute.
Add in the chopped onions, chopped green chillies, and diced capsicum.
Mix well, Do not burn the onions. Cook them until they are translucent. You can add a bit of water if required.
Add in Teriyaki sauce, chilli sauce, and vinegar. Mix well.
Make a slurry of 1 tbsp cornflour with 1 tbsp water. Add it to the sauce and cook until you get a coating consistency.
Add in the fried prawns. Mix well so that the prawns are well coated. Adjust the salt if needed.
Serve hot garnished with chopped spring onion greens and sesame seeds.