Cook the tortellini according to package instructions. Drain and set aside.
In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 3-4 minutes.
Add the minced garlic and sliced mushrooms to the skillet. Cook for an additional 5-7 minutes, or until the mushrooms are tender and browned.
Stir in the fresh spinach and cook until wilted, about 2 minutes.
Pour in the heavy cream and add the Italian seasoning, salt, and pepper. Stir to combine and let simmer for 2-3 minutes.
Add the cooked tortellini to the skillet and toss gently to coat in the creamy sauce.
Stir in the grated Parmesan cheese until melted and well combined. Remove from heat.
Serve warm, garnished with chopped parsley.