Prepare the Filling: Place a large skillet over medium-high heat and add a teaspoon of olive oil. Add the ground beef and break it up with a spatula. Cook until it is no longer pink. Once browned, drain the excess liquid and fat from the pan.

Sauté the Vegetables: Push the beef to one side of the skillet or remove it temporarily. Add the diced onions and bell peppers to the pan. Sauté them for about 4 to 5 minutes until they become soft and slightly translucent. Mix the vegetables back in with the beef.

Season the Mixture: Sprinkle the taco seasoning over the beef and vegetable mixture. Add two tablespoons of water to help the spices coat everything evenly. Stir well and let it simmer for 2 minutes until the liquid evaporates. Remove the pan from the heat and stir in the fresh cilantro if you are using it.

Assemble the Quesadillas: Wipe the skillet clean or use a fresh griddle. Place one tortilla on a flat surface. Sprinkle a generous layer of cheese over one half of the tortilla. Spoon a portion of the beef and pepper mixture over the cheese, then add another small sprinkle of cheese on top. Fold the tortilla in half.

Toast to Perfection: Lightly brush the skillet with a tiny amount of olive oil and set it to medium heat. Place the folded quesadilla in the pan. Cook for about 2 to 3 minutes on the first side until it reaches a deep golden brown. Carefully flip it with a large spatula and cook the other side for another 2 minutes.

Slice and Serve: Remove the quesadilla from the pan and let it rest for one minute. Use a pizza cutter or a sharp knife to slice it into triangles. Repeat the process for the remaining Easy Beef Quesadillas.