Cook bacon in skillet until crispy. Transfer to a paper towel lined place to drain.
Heat griddle or skillet over high heat until smoking. (I recommend a flat cast iron griddle and an outdoor grill. Things are about to get smokey).
Arrange melted butter in a bowl next to a dish with the blackening spice.
Coat the chicken in butter, then cover in the spice.
When the griddle surface is smoking, turn on a fan for ventilation and add the chicken.
Cook for 5 to 7 minutes, turning as needed until all sides are blackened and chicken is cooked through. Remove from griddle and cover while preparing the macaroni.
In a large pot of salted boiling water, cook pasta according to directions on box; Drain and set aside.
In a medium saucepan over medium heat, melt the butter and whisk in the flour.
Cook for 1 minute. Slowly whisk in the cream and milk. Add the cheese and stir until melted through.
Toss cheese sauce over pasta. Add the frozen peas and bacon.
Place heaping portions of macaroni and cheese on plate, top with chicken and scallions.