This one-pan casserole can be prepped and baked in an oven-safe skillet and makes great leftovers. Smarts: Nutritional yeast is a paleo-friendly condiment that can be found at specialty food stores and even many standard grocery stores now. It has a savory, nutty flavor that many people think resembles the flavor of parmesan cheese. If you've never tried it, see if you can buy a small amount from the bulk bins to test in this recipe, but the recipe is still satisfying even without it!
Heat oven to 350F / 177C. Place one oven rack in the upper third of the oven and another in the lower third.
Brush a sheet pan with some oil or spray with nonstick cooking spray. Toss mushrooms with olive oil, thyme and some salt. Spread out on sheet pan. Roast on the top rack of the oven, shaking the pan halfway through cooking, until mushrooms are golden brown and tender, 25 minutes.
While mushrooms roast, heat a large skillet over medium-high heat. Add cooking oil and then onions. Saute until onions are soft, 3 to 4 minutes. Add chicken and saute until chicken is cooked on the outside (don’t worry if it isn’t cooked all the way through), ~3 minutes more.
Remove skillet from the heat and stir in cauliflower rice, broccoli, stock and nutritional yeast (if using). (You can bake the casserole right in the skillet or transfer it to a baking dish if you prefer.) Cover tightly with foil.
Bake casserole on the lower rack of the oven until the chicken is cooked through, ~25 minutes.
When casserole and mushrooms are finished, squeeze lemon juice over top of mushrooms.
Serve casserole with some hot sauce on top if you’d like. Enjoy mushrooms on the side.