Trout is a wonderful alternative to salmon. It is sustainable, local, and forgiving when cooked. Enjoy the crispy skin without worrying about scales. The skin comes off easily after cooking, if not wanted. To reduce the fishy smell from cooking inside the house, I always cook fish in the oven to contain the cooking vapours.
Cook the potatoes until soft in boiling salted water. Drain and set aside until needed.
Preheat the oven to 400°F
Peel and slice the red onion. Wipe off the trout. Trim the fatty belly, if needed. Cut the fillet in half and place on a plate or tray. Oil, salt, and pepper the fleshy side, turn them over and repeat on the skin side. Leave skin side up while waiting to cook it.
Combine chopped parsley and capers with grainy mustard and lemon pepper vinaigrette. Quarter the potatoes.
Heat a cast iron pan, large enough for the potatoes to lay in a single layer, over a medium heat. When hot, add 2 tbsp oil and the red onions, then season with salt and pepper. When the red onions begin to caramelize, add the cooked potatoes, toss gently, and put in the oven. Toss occasionally.
Heat a second pan, large enough to hold the trout, over medium high heat. When the pan is hot, add enough oil to cover the bottom of the pan (approx. 2 tbsp). Allow to heat briefly then carefully add the trout skin side down. The oil should spatter a bit. Once pieces are in the pan, place in the oven to cook.
The trout will cook most of the way on the skin. As it cooks the flesh lightens, allow this to reach almost to the top of the fillet. Once almost cooked through, remove the pan from the oven, flip the pieces over and allow to cook on top of the stovetop using the residual heat from the pan.
Remove the potatoes from the oven, add the caper parsley dressing mix and toss well. When all coated add the arugula and continue to toss allowing the arugula to wilt. If the pan is too heavy to toss using a pair of tongs works well for this.
Portion the potatoes mix onto 4 plates and top with the trout. If there is any extra liquid in the potato pan use a spoon and drizzle it onto the trout.