Preheat your oven to 400°F (200°C).

In a large bowl, combine olive oil, chopped sage, garlic powder, salt, and pepper. Add the chicken breasts and coat them well with the marinade. Let them marinate for at least 30 minutes.

In a skillet over medium heat, add the marinated chicken breasts and sear for 3-4 minutes on each side until golden brown. Remove the chicken and set aside.

In the same skillet, add the sliced cremini mushrooms and sauté until they are tender and have released their moisture, about 5-7 minutes.

Pour in the heavy cream and bring to a simmer. Stir in half of the grated Parmesan cheese, and cook until the sauce thickens slightly, about 3-4 minutes. Season with salt and pepper to taste.

In a baking dish, place the seared chicken breasts and pour the mushroom cream sauce over them. Top with the remaining Parmesan cheese.

Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and the cheese is bubbly and golden brown.

While the chicken is baking, prepare the crispy shallots. Heat vegetable oil in a frying pan over medium-high heat. Dredge the thinly sliced shallots in flour, shaking off any excess. Fry them in batches until they are golden brown and crispy, about 2-3 minutes. Drain on paper towels and season with salt.

Once the chicken is done baking, remove it from the oven and let it rest for a few minutes. Serve topped with crispy shallots and additional sage, if desired.