Prepare the vegetables. Cut the red potatoes in quarters. Peel and trim the baby carrots. Trim and cut the spring onions in half lengthwise. Peel and quarter the turnips.
In a medium saute pan, over high heat, add the olive oil. Add the prepared vegetables, sprig of thyme and saute for about 2 minutes. Season with salt and pepper and add butter. Continue to saute until lightly golden, another 2 to 3 minutes. Transfer to a preheated oven and roast for about 10 minutes or until caramelized.
Meanwhile, make 3 diagonal slices on each side of the trout. Season with salt and pepper inside and outside. Dredge in flour. In a large saute pan, over high heat, add 2 ounces of butter. Pan-fry the prepared trout until golden, about 5 minutes. Turn and add a sprig of sage and the remaining 1-ounce of butter. Continue to pan-fry until golden on both sides, basting the topside of the fish with the cooking butter, another 5 minutes.
Add lemon juice and parsley. Add the cooked vegetables to the trout and serve on pan for an informal al fresco dining, or on heated serving plates, place a pan-fried trout and surround with half of the caramelized vegetables. Sprinkle with parsley. Serve with lemon wedges on the side and serve immediately.