Gather all ingredients.

Heat 2 teaspoons oil in a 10-inch skillet over medium heat. Add onion and bell pepper; cook and stir until softened, 5 to 10 minutes. Season with salt and transfer to a bowl.

Brush 1 side of each tortilla with remaining oil. Place 1 tortilla, oil-side down, in the same skillet; sprinkle with 1/2 the steak, 1/2 the onion mixture, and 1/2 the Mexican cheese mixture.

Place a second tortilla, oil-side up, onto cheese layer, pressing down with a spatula to seal.

Cook quesadilla over medium heat until cheese melts and tortillas are browned, 3 to 4 minutes per side.

Remove quesadilla from skillet and cut into wedges. Repeat with remaining ingredients for second quesadilla.