Heat just half of the oil in the skillet over medium-high heat. Add diced steak and season with some salt and pepper. Cook until browned and cooked to your liking. Transfer steak to a plate and set aside.

Add mushrooms, onions, just half of the chili powder, and some salt and pepper to the same skillet. Cook until veggies soften and start to brown, 5-8 minutes. Transfer veggies to a plate and wipe the skillet clean.

Make the crema by mixing the sour cream with the remaining half of chili powder in a small bowl. Stir in a small splash of water until it reaches a sauce-like consistency. Set aside.

Evenly sprinkle cheese on half of the tortilla. Top with veggies and steak. Fold tortilla in half to create the quesadilla.

Heat remaining oil in a skillet over medium heat and add the quesadilla. Cook until tortilla is browned and cheese is melty, about 3-5 minutes per side.

Cut quesadilla into wedges and serve with crema.