Heat olive oil in a large skillet over medium-high heat. Add steak, bell peppers, and onion and cook until steak is cooked through and vegetables are tender.
Add taco seasoning and stir to combine.
Lay out two tortillas on a work surface. Top each with half of the steak mixture and sprinkle with cheese.
Top with remaining two tortillas and press down gently.
Heat a large nonstick skillet over medium heat. Place quesadilla in the pan and cook for 2-3 minutes per side or until golden brown.