To prepare the quesadillas: Slice the chicken breast into thin strips. Cut the onion and green pepper into thin strips, and slice the mushrooms thinly. Heat a skillet over medium heat with a little olive oil, season the chicken with salt and pepper, and sauté until cooked through. Remove the chicken to a plate and set aside.

In the same skillet, add the onion and green pepper, season with salt and pepper, and cook until softened. Add the mushrooms and cook for a few more minutes. Once the vegetables are cooked, add the reserved chicken, mix well, and cook everything together for a couple of minutes. Transfer to a bowl and set aside.

Place a large skillet over medium heat. Lay one flour tortilla in the skillet, spread some of the chicken and vegetable mixture on top, and cover generously with shredded cheese. Top with another tortilla. Cook for a couple of minutes until the cheese starts to melt. Place a plate on top and carefully flip the quesadilla, then cook the other side until golden brown. Remove from the skillet and cut into 4 pieces.

To prepare the guacamole: Peel the tomato and dice it into small cubes. Finely chop the onion or scallion and set aside.

Finely chop the cilantro and set aside. In a large bowl, scoop the avocado out of the skin with a spoon and mash with a fork until chunky. Add the tomato, onion, cilantro, a squeeze of lime juice, salt and pepper to taste, and a drizzle of olive oil. Mix well and transfer the guacamole to a serving bowl.

Serve the quesadillas hot with guacamole and some tortilla chips. Enjoy this delicious platter to share!