Optionally sear the salmon: heat a small non-stick skillet over high heat with a little olive oil and sear fillets skin-side down for 1 minute; set aside. This step is optional—you can also cook directly in the Instant Pot.
Set the Instant Pot to Sauté. Add the olive oil, light brown sugar, fish sauce, soy sauce, grated ginger, lime zest and juice, white pepper, and water. Cook, stirring, for about 1 minute until the sugar dissolves and the mixture is bubbling.
Add the sliced garlic and sliced red chilli (if using) and cook for 30 seconds more, then press Cancel to stop Sauté mode.
Place the salmon fillets in the inner pot, skin side up (or skin side down if you prefer); spoon some of the sauce over the fillets.
Secure the lid, set the valve to Sealing, select Pressure Cook on Low pressure for 1 minute, and ensure Keep Warm is off.
When cooking finishes, allow a 5-minute natural pressure release, then carefully turn the valve to Venting to release any remaining pressure. If the salmon is underdone, use Sauté until it reaches your preferred doneness.
Carefully remove the salmon and arrange flesh-side up on a platter. Return the inner pot to Sauté mode and simmer the sauce for about 1 minute, or until slightly thickened.
Spoon the reduced sauce over the salmon and garnish with chopped spring onions, fresh coriander and lime wedges. Serve immediately.
