Preheat oven to 350 degrees. Toss mushroom ingredients together on a rimmed baking sheet.
Heat olive oil in a Dutch oven over medium low heat. Add garlic and arborio rice. Sauté until the garlic starts to smell and the pan looks dry. Add wine; stir and let it sizzle out. Add 2 1/2 cups of the chicken stock. Bring to a simmer.
Put a lid on the risotto pot. Transfer both pans to the oven (risotto on top, mushrooms on bottom). Bake for 14-15 minutes. Remove the risotto pot, but let the mushrooms keep roasting – increase to 400 degrees, and bake for another 5-8 minutes, until golden brown.
Place risotto back over a medium low heat. Slowly add in remaining 1-or-so cups of chicken broth, stirring between additions until nice and creamy. Stir in the Parmesan, unsalted butter, lemon zest, lemon juice, and no-salt substitute. Stir in 2 cups spinach until wilted and mixed well. Add in the mushrooms and serve.