In a medium bowl, combine the olive oil, light brown sugar, fish sauce, soy sauce, grated ginger, lime zest and juice, white pepper, and water. Whisk until the sugar is mostly dissolved and the mixture is well combined.
Turn on your Instant Pot and select the 'Sauté' function. Add the finely sliced garlic and optional red chili. Sauté for 1-2 minutes until fragrant, making sure not to burn the garlic.
Carefully place the salmon fillets in the Instant Pot, skin side down if applicable. Pour the prepared sauce over the salmon, ensuring each piece is well coated.
Secure the lid on the Instant Pot and set the valve to sealing. Use the 'Manual' or 'Pressure Cook' setting and cook on high pressure for 3 minutes. Once the cooking time is up, allow for a natural release for 5 minutes, then carefully switch the valve to venting to release any remaining pressure.
Carefully remove the salmon from the pot and transfer to a serving dish. Drizzle with the remaining sauce from the pot. Garnish with chopped spring onions and fresh coriander. Serve with extra lime wedges on the side for a zesty kick.
