Optimizing for efficiency: boiling frozen salmon without defrosting
The problem will be one of temperature difference. The outermost mm of your salmon will thaw immediately but the innermost one will still be raw. 

Some meat thermometers will work in water but i doubt that they will be accurate in a thin filet as they are mostly for use in large chunks of meat.

So the only good way to check fore done-ness is to cut the filet in two and check the texture yourself. If it starts to "flake" (i.e. the meat fibers start to separate) it is done. Ideally you will be able to "break" a filet cleanly in two. But do that too often and you'll end up with salmon soup. 

So my recommendation: oven-roast your salmon. There will be two advantages: one is that you can easily check the inside and pop it back in the oven if you are not satisfied. On the other hand its easier to make tasty salmon in the oven. You can even work in a herb-crust or something like it.
Health-wise they are exactly the same as long as you don't start drenching the fish in oil.

Another option could be to poach the fish in a ziplock bag. It will take a bit longer as the heat circulation will be slightly worse but locks in the flavor, gives you the option of adding some herbs and the option the measure the done-ness without creating a mess.