Place a large non-stick skillet over medium heat. Add spinach then immediately begin tossing and stirring until it begins to wilt and release water.

Once spinach is wilted and dark green in color, add steak sauce and sliced steak. Heat until meat is warmed over and most of the liquid has evaporated. Transfer to a paper towel-lined plate to absorb excess moisture.

Wipe out skillet then return to medium heat. Let a few seconds pass so the skillet can return to temperature then lightly coat with cooking spray. You can alternately brush a very light amount of butter onto the bottom of the pan. Place a tortilla in the skillet then immediately add ½ cup of shredded pepper jack cheese to cover one half of the tortilla. Spread roughly ¼ of the steak and spinach mixture on top of the cheese then fold the uncovered half of tortilla on top of side with steak and cheese.

Press down on the quesadilla using a spatula to force filling and cheese into contact with heat and to seal top and bottom together. Let tortilla to cook on the first side for about 2–3 minutes (depending on temperature), until golden brown and crispy.

Flip quesadilla then cook for 2–3 minutes until golden brown and crispy on the opposite side. If the tortilla becomes too brown before the cheese melts, lower the temperature. The objective is for the cheese to be completely melted and gooey at the same time the tortilla becomes golden and crispy. Generally, if you have the patience for it, lower heat is better.

Transfer to a cutting board, cut into wedges then serve with extra steak sauce on the side for dipping.