Season the boneless, skinless chicken breasts with salt and pepper. Heat a skillet over medium heat, add the chicken and cook for about 6-7 minutes per side until golden brown and cooked through. Remove from heat and let rest before shredding.

In a large pot, bring salted water to a boil. Add the macaroni and cook according to the package instructions, usually around 7-8 minutes, until al dente. Drain in a colander.

In a medium saucepan, melt 4 tablespoons of butter over medium heat. Stir in 4 tablespoons of flour, cooking for about 1 minute. Gradually whisk in 2 cups of milk, stirring constantly for 5-7 minutes until the sauce thickens.

Reduce the heat to low and stir in 1 cup of shredded cheddar cheese and 1 cup of shredded mozzarella cheese until fully melted and smooth. Adjust seasoning with salt and pepper.

In a large mixing bowl, combine the shredded chicken, cooked macaroni, and 1 cup of BBQ sauce. Pour the cheese sauce over and stir gently to coat everything.

Transfer to a serving dish and garnish with more BBQ sauce or chopped herbs. Serve warm.