Pat steak dry and season with 1/2 tsp salt and 1/2 tsp black pepper.
In a large deep skillet, heat olive oil over medium-high heat until shimmering. Sear steak bites in batches for 2 minutes per side until browned but medium-rare. Remove steak and set aside.
Reduce heat to medium. Add butter to the skillet, scraping up any browned bits (fond). Stir in minced garlic and cook for 1 minute until fragrant.
Whisk in beef broth and heavy cream. Bring to a gentle simmer.
Add refrigerated tortellini to the sauce. Cover the skillet and cook for 5 to 7 minutes, or until the pasta is tender and the sauce has reduced slightly.
Stir in the Parmesan cheese until melted and smooth. Add the fresh spinach and cook for 1 to 2 minutes until wilted.
Add the seared steak bites back into the skillet. Toss to coat and heat through for 1 minute.
Season with remaining salt, pepper, and red pepper flakes before serving.