Place the stock in a pot and set over medium-low heat. Preheat the oven to 425 degrees F. Line a 9” x 13” baking dish with parchment paper and set in the salmon. Drizzle the fish with lemon juice and 1 1/2 Tbsp. of the olive oil. Season with salt and pepper and set aside.
Pour the remaining oil into a second pot and set over medium heat. Add the onion and cook 2 to 3 minutes. Add the rice and cook 2 to 3 minutes more. Add the wine and simmer until it is almost fully absorbed by the rice. Add 1 cup of the stock, adjusting the heat upwards or downwards so that the liquid gently simmers, and cook until the stock is almost fully absorbed by the rice. Add the remaining stock, 1 cup at a time, making the next addition when the rice has almost fully absorbed the last, and cook until the rice is tender. You may not need all the stock.
When you are 15 minutes into cooking the risotto, bake the salmon for 15 minutes, or until just cooked through.
When the rice is tender, mix in the asparagus, cheese, salt and pepper and heat through 2 to 3 minutes. Divide the risotto among 4 plates. Set a piece of salmon on top of the risotto, garnish with lemon slices and serve.
Note: To blanch the asparagus, plunge in boiling water 1 minute. Drain well, cool in ice-cold water and drain well again.