Preheat oven to 345 degrees.
Bring 2 cups of water to a simmer. Add rice and butter to another pan. In separate pan, add mushrooms and 2 tablespoons of butter and sauté until golden brown. Turn on heat, and stir. As rice and butter start to sizzle, add white wine, stirring constantly. When white wine has reduced to syrupy consistency, start adding hot water, 1/4 cup at a time, still stirring constantly, until the water has again reduced to a syrupy consistency. Repeat this process and taste rice until desired consistency has been reached. (about 17 minutes) Turn off heat, and whip in the parmesan and mascarpone (if using). Stir in the mushrooms, and season with salt and white pepper to taste.
Meanwhile crush one large handfuls of arugula and blend on high with a 1/4 cup of canola oil, 1 tablespoon of cup parmesan cheese, and cracked pepper for 3 minutes. Add in salt and 1 tablespoon rice vinegar, blend for another second and set aside.
Lay salmon on a baking sheet and season with salt and pepper. Roast in the oven for 5-8 minutes, until salmon starts to softly break apart when you push on them with you finger.
Toss shaved radishes and arugula in a large bowl with a drizzle of olive oil, rice vinegar and a pinch of salt. Divide risotto between two plates, top with salmon and arugula salad and drizzle with arugula vinaigrette.