Preheat the oven to 425 degrees F. Lightly grease an oven-safe skillet with olive oil.
In a medium bowl, mix together the ricotta, gouda, 1 tablespoon thyme, 1 tablespoon sage, nutmeg, and a pinch of salt and pepper.
Gently loosen the skin from each chicken breast using your fingertips. Stuff about 2 tablespoons of the ricotta mixture under the skin of each breast. Rub the chicken skin with olive oil and season with the remaining thyme, sage, salt, and pepper. Place the chicken in the prepared skillet. Arrange the shallots, garlic, and mushrooms around the chicken. Drizzle olive oil over the mushrooms and season with salt and pepper. Roast in the oven for 20 minutes, until the chicken is cooked through.
Remove the skillet from the oven and transfer the chicken and mushrooms to a plate.
Place the skillet with shallots and garlic over medium heat. Add the butter and cook for 1-2 minutes, until it begins to brown. Pour in the vegetable broth and apple cider, then bring to a boil over high heat. Let it boil for 5 minutes, until the liquid reduces by half. Return the chicken and mushrooms to the skillet and simmer for 1 minute. Remove from heat.
While the sauce is simmering, prepare the mashed cauliflower. Bring a large pot of water to a boil. Add the cauliflower florets and cook until tender, about 10 minutes. Drain thoroughly.
In a food processor, combine the cooked cauliflower, smashed garlic, cream cheese, and butter. Season with salt and pepper to taste. Pulse until smooth and creamy, about 1 minute.
To serve, spoon the mashed cauliflower onto plates, add the chicken and mushrooms, then spoon the pan sauce over the top. Garnish with fresh thyme and enjoy!