only potential problem I could foresee is the highly aromatic elements - esp onions, lemongras and powerful basil - might completely overpower the salmon's subtler essence.

Use it raw as a garnish. Sliced thin (under 1/8") and give each serving about half a circular slice from the onion. That way, your guests can enjoy as much or as little onion flavor as they wish.

If it is the caramelized onion taste you want, then you might consider sweet yellow, Heat butter in the skillet, and carefully lay in a cross slice of onion. Let it brown and turn translucent, and then lift it out with the spatula and place it as whole as possible on the presentation.

The times I've had salmon with a prominent seasoning, its never been as tasty as when I had it mostly plain. That goes with a few other seafoods I can think of too. But I might just prefer my seafood as simple as possible, its all about subtle flavor and texture for me. Or there might be other fishes that work well with heavy seasoning. Take my ideas with a grain of salt though, I've NEVER cooked seafood before, heheh.