Toss birds eye chilies, red capsicum, garlic, oil, malt vinegar, paprika, oregano, onion powder, sugar, and salt into blender. Blend until smooth and saucy.
Slather chicken with peri peri sauce, cover, and marinate in fridge for at least 2 hours or overnight for best flavor.
Pour a little olive oil in pressure cooker and place chicken inside with some leftover sauce. Lock lid and set sealing ring properly.
Set cooker to high pressure and let build for about 10 minutes. Cook chicken at full pressure for 8 minutes.
Use quick release method gently to release steam quickly without drying chicken. Remove lid once pressure drops.
Toast buns lightly, pile on lettuce and tomato slices, spread mayo mixed with sour cream if desired, and drizzle extra peri peri sauce.
Assemble burger with chicken and toppings, slam bun on top and serve.
Enjoy your juicy, tender peri peri chicken burger fresh and flavorful.