Pour Saute on the Instant Pot and pour in 1 cup of water. Let the water simmer.
Toss the prawns, red bell pepper slices and green beans in a bowl together with the spices and fish sauce. Transfer to the Instant Pot Steamer basket and lower down to the inner pot. Cover with the glass lid and Steam on High for 5 minutes.
Meanwhile, mix gata mix with water and sugar.
Once steaming is done. Lift out the steamer basket. Pour in tomato chunks and gata mix in the pot. Let the residual heat cook them. Adjust seasoning if needed.
Transfer steamed shrimp and vegetables on a container and pour the sauce over.