Whisk together olive oil, soy sauce, and steak seasoning in a small, shallow dish. Add steak strips and marinate for 30 minutes.

Heat a heavy cast iron skillet over medium-high heat. Add butter. Cook steak strips in the melted butter, until browned, about 2 minutes per side. Add mushrooms and cook until softened, about 5 minutes.

Meanwhile, fill a large pot with lightly salted water and bring to a rolling boil; stir in tortellini and return to a boil. Cook uncovered, stirring occasionally, until the tortellini float to the top and the filling is hot, about 3 minutes.

Melt butter for Alfredo sauce in a saucepan over medium heat. Stir with a wooden spoon and add heavy cream. Stir until combined. Add Parmesan cheese to the cream mixture in the saucepan and stir until blended. Season with nutmeg.

Drain tortellini, return to the pot, and toss with Alfredo sauce to coat. Serve tortellini topped with steak and mushrooms.