Put the potatoes in a pan of cold water, then bring to the boil. Simmer for 10-15 minutes, until tender, then drain.
Meanwhile, thinly slice the onion and chop garlic.
Heat some oil a small frying pan and fry the onion over low heat for 8 minutes, stirring regularly.
When the onion has softened add the garlic and stir for a minute.
Add the balsamic vinegar, turn the heat up a little and caramelise the onion.
Put the potatoes into a large bowl and cut them into bite-sizes pieces. Drizzle with some olive oil and season with salt and pepper.
Drain the salmon and add to the potatoes. Combine well.
Add the caramelised onion and garlic, then the lemon juice and zest.
Add the chopped herbs, toss and serve.