Wash the spring greens in cold water, then put them in a large pan over a medium heat. Cook for 4-5 minutes (the residual water will provide enough moisture to steam them), stirring occasionally, until wilted and tender. Set aside.
Cut the salmon fillet into thick slices, then cut each slice in half.
Put a wok over a medium-high heat and add 2 tbsp sesame oil, then the chillies. Stir-fry for a few minutes or until they slightly blacken, then add the onion, garlic and ginger. Stir-fry until the onions soften. Turn up the heat, then add a splash of oil along with the salmon. Stir-fry for 1-2 minutes until it starts to colour.
Add the wilted greens, soy and sherry and stir-fry for another minute or two to heat through.
Discard the chillies, then divide the stir-fry among plates and scatter over the seeds, if using. Add a good squeeze of lime to each, then serve with noodles or rice, if you like.