Spray a skillet with cooking spray, and place over medium heat. Fry chicken breasts in the skillet until cooked through, about 20 minutes.
While the chicken cooks, melt butter in a small skillet over medium heat, and stir in flour until smooth. Stir in green onion, and cook, stirring constantly, until the mixture starts to brown. Gradually mix in milk, and continue cooking and stirring until the sauce is thick and smooth. Remove from heat, and stir in the mustard and Camembert until melted and smooth.
Remove chicken to serving plates, and top with slices of avocado. Pour sauce over the chicken, and serve.
