Begin by heating vegetable oil in a spacious skillet over medium heat. Arrange the steak evenly on the skillet, seasoning it with taco seasoning. Saute each side of the steak for about 1-2 minutes until it obtains a slight browning. Next, introduce the red bell pepper and onions, sautéing them along with the steak for approximately 5-7 minutes until the steak is fully cooked and the vegetables reach desired tenderness. Once done, generously top the steak and vegetables with salsa, ensuring thorough coating, and sauté for a few more minutes to meld the flavors. Remove the skillet from heat.

Meanwhile, preheat a griddle over medium-high heat or alternatively, utilize a cast iron skillet. Place the tortillas on the heated surface. Distribute a modest portion of each cheese onto each tortilla, followed by layering steak and vegetables, and then topping with more cheese. Carefully fold each tortilla in half to form a half-moon shape.

Cook until one side of the tortilla turns golden brown, approximately 1-2 minutes. Flip and continue cooking until the other side achieves a similar golden hue, again, for about 1-2 minutes. Keep a close eye on them as they brown quickly. Once done, transfer the quesadillas onto a cutting board, slice, and they are ready to be served and enjoyed!

Additional Tips:

Store any leftovers in an airtight container in the refrigerator for up to 5 days.

While top sirloin is recommended for this recipe, flank steak can be used as an alternative if preferred.