Creating this Chicken, Spinach, and Mushroom Low-Carb Oven Dish is simple if you follow these steps:

1. Preheat the Oven: Begin by preheating your oven to 375°F (190°C).
2. Sauté Vegetables: In a skillet, heat the olive oil over medium heat. Add the chopped onions and garlic, sautéing until fragrant and translucent, about 3-4 minutes.
3. Add Mushrooms: Toss in the sliced mushrooms to the skillet. Cook until they are browned and tender, around 5-7 minutes.
4. Stir in Spinach: Add the chopped spinach to the skillet and cook for an additional 2-3 minutes, just until wilted.
5. Season the Mixture: Sprinkle in the Italian seasoning, salt, and pepper, mixing well. Remove from heat and set aside.
6. Prepare Chicken: In a baking dish, arrange the chicken breasts in a single layer. Season with salt and pepper.
7. Layer the Vegetables: Spread the sautéed vegetable mixture evenly over the chicken breasts.
8. Add Cheese: Sprinkle the shredded mozzarella and grated Parmesan cheese over the top of the vegetables.
9. Bake: Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for another 10-15 minutes, until the chicken is cooked through and the cheese is bubbly and golden.
10. Serve: Once done, let it rest for a few minutes before serving.

These steps will guide you effortlessly in cooking this incredible dish!