Heat a large skillet over medium high heat. Spray with cooking spray.
Add steak to pan and sprinkle with ⅛ teaspoon of salt. Cook 3-4 minutes or until browned, then transfer to a medium bowl.
Add butter to pan. Once melted, add remaining ¼ teaspoon salt, minced garlic, and mushrooms. Cook 5-6 minutes until mushrooms begin to reduce (get smaller.) Add mushroom mix to steak.
Wipe the pan clean. Toast tortillas on one side, then flip and fill with steak mixture and a scattering of cheese. (1/3 cup) Cover with another tortilla. Let cheese melt enough to allow you to flip the tortilla in the pan without losing all the goodness inside.