Remove steaks from fridge 5 minutes before cooking; slice mushrooms and mince garlic.
Heat olive oil in a large skillet over medium-high heat, season steaks with salt and pepper, then sear for 3 minutes per side for medium-rare; transfer to a plate.
In the same skillet, sauté mushrooms and garlic for 4 minutes until mushrooms release moisture, then add balsamic vinegar and cook 1 minute more.
Add spinach to the mushroom mixture and stir for 1 minute until wilted.
Divide mushroom-spinach mixture among plates, top with one steak per plate, and serve immediately.
Photo: Andre Davis / Unsplash