Pour chicken bone broth (or low-sodium stock) into a small sauce pan. Set the pan over low heat, and keep warm while you make the risotto.
Heat olive oil in a separate pan. Stir in finely chopped onions with a pinch of salt, and cook the onions until very soft and lightly charred, about 10 minutes.
Stir in garlic, and cook for about 30 seconds until fragrant.
Pour in dry arborio rice. Stir to coat it in the onions and garlic, and cook for 2-3 minutes until only a small white dot remains in the center of the rice grains.
Stir in white wine until absorbed, about 1-2 minutes.
Pour one ladle of warm broth into the pan with the rice. Stir frequently until the broth is nearly absorbed. Repeat this step, one ladle of broth at a time, until all of the broth is absorbed into the rice. This takes about 20-25 minutes total, and the texture of the rice will become very soft and creamy. *It's ideal to prepare the salmon about halfway through cooking the risotto, so they are both ready around the same time*
Stir in lemon zest, mascarpone, and parmesan until fully combined.
Stir in peas and fresh lemon juice. Taste the risotto, and add more salt, pepper, or lemon juice if desired. Allow the risotto to rest while you make the salmon.