Remove the stems and seeds from the peppers and cut them into 5-7mm (¼") thick strips.
Top and tail the red onion, then cut it in half, peel it and then cut it into slices 5-7mm (¼") thick.
Cut the spring onions into thin (2-3mm or ⅛") rings.
Peel the garlic and then cut it into slices as thin as you can.
Mix all of the ingredients for the sweet and sour sauce, with the exception of the water and the cornflour, in a bowl.
Mix the cornflour with the water in a small bowl
Heat 2 frying pans over a high heat and add a tablespoon of oil to each pan, try and use a nonstick pan for searing the salmon.
When the pans are hot, add the red onion and peppers to one of the pans and stir-fry for 3 minutes.
After the veggies have been cooking for 1 minute, add the salmon fillets to a second pan and sear skin side down for 4 minutes.
Add the sugar snap peas and garlic to the veggies and cook for a further 1 minute.
Flip the salmon and add the veggies to the pan with the salmon, and pour in the sweet and sour sauce. Make sure you do not pour the sauce over the skin of the fish; we want to keep this nice and crispy.
Cook for 2-3 minutes, then remove the salmon and set it aside.
Pour the cornflour slurry into the sauce and cook until the sauce thickens, making sure that you stir constantly.