Preheat the skillet: Set a large skillet over medium-high heat. Add the olive oil.
When it shimmers, add the mushrooms in an even layer. Don’t stir for 2–3 minutes so they can brown.
Brown the mushrooms: Stir and continue cooking until they release their liquid and turn golden, 6–8 minutes total. Add the butter for extra caramelization if you like.
Season with a pinch of salt. Transfer mushrooms to a plate.
Sauté onion and garlic: In the same skillet, add the diced onion. If the pan looks dry, add a splash of oil.
Cook 3–4 minutes until translucent. Stir in garlic and cook 30 seconds until fragrant.
Cook the turkey: Add ground turkey, breaking it up with a spatula. Season with salt, pepper, thyme, and smoked paprika.
Cook until no longer pink and edges start to brown, 6–8 minutes. Don’t crowd the pan—let some bits crisp for flavor.
Deglaze and season: Pour in Worcestershire sauce and scrape up any browned bits. Return the mushrooms to the pan and stir to combine.
Add broth and simmer: Pour in the chicken broth.
Bring to a gentle simmer for 2–3 minutes to marry the flavors. For a thicker sauce, stir in the cornstarch slurry and simmer 1–2 more minutes until glossy.
Melt the Swiss: Reduce heat to low. Lay Swiss slices over the top or sprinkle shredded cheese evenly.
Cover for 1–2 minutes until melted and gooey.
Finish and serve: Taste and adjust salt and pepper. Sprinkle with chopped parsley. Serve over rice, mashed potatoes, pasta, or toast, or keep it simple and eat straight from the skillet.