I cooked this salmon in an outboard engine on a boat. I was lucky. The heat generated during our short trip was just enough to cook the fish. It was fun, but all in all I recommend using an oven.
The cucumber salad: Put the cucumber slices in a bowl and sprinkle with sea salt. Cover the bowl and shake it for a few seconds, allowing the salt to cover as much of the cucumber as possible. This process extracts some of the moisture, making the cucumber more susceptible to other flavors. Add the celery, red onion, vinegar, mustard seeds and sugar. Cover and shake the salad again until mixed.
The river trout: Spread out the flour on a large plate and sprinkle with salt. Turn the trouts in the flour and salt. Fill the cavity of the fish with fresh mint.
Heat the butter in a medium frying pan over medium high heat until melted and foamy, but not brown. Place the fish in the frying pan and sear for 5-6 minutes on each side until crispy and golden brown. (The exact length of time depends on how big your fish is. The fish is done when the flesh flakes easily when poked with a fork.)
Transfer the fish to serving plates. Add the sour cream to the frying pan. Using a spatula, scrape out the solids that have formed on the bottom, and stir them into the sour cream. Let the sauce simmer for 30- 60 seconds, allowing it to thicken a little. Drizzle the sauce over the fish and serve with cucumber salad.