2. Heat the stock in a saucepan, season well with salt and pepper, and keep hot over low heat.
3. Heat the olive oil over medium heat in a separate medium-sized pot. Add the onion, season lightly with salt and pepper, and cook until it turns translucent, about 5 minutes.
4. Turn the heat to high, add the shrimp and season with salt, pepper, garlic and lemon zest. Cook the shrimp until they are just opaque, about 2 minutes. Transfer the shrimp to a plate and set aside.
5. Add the rice to the onions in the pot, stir and turn the heat to low. Add about 1 cup of the hot stock to the rice mixture and stir slowly until the stock is absorbed. Continue to add the stock 1 cup at a time, stirring slowly, letting the rice absorb the stock before adding more.
6. The risotto is cooked when it is creamy on the outside and slightly firm (al dente) in the center, about 20 to 25 minutes in all. Stir in the shrimp, half of the Parmesan cheese and half of the asparagus. Season with salt and pepper to taste. If the risotto is too thick, add a little more stock until it becomes creamy.
7. Divide the risotto into serving dishes and sprinkle with the remaining cheese and asparagus.