Preheat oven to 375°F.
Line a 9-inch by 9-inch pan with foil. Set aside.
In a large skillet, melt butter over medium heat. Once butter is melted, add flour and whisk until it forms a paste. Slowly pour in the milk, whisking constantly. Once the milk has been added and there are no clumps, cook until thickened, or about 10 minutes. Add cheese to the sauce gradually, whisking as it melts. Season with salt, pepper and Sriracha sauce and mix thoroughly. Try some out and adjust seasonings according to taste.
Add the chicken and pasta and mix gently to combine.
Pour into prepared baking pan and top evenly with breadcrumbs. Spray top with cooking spray and place pan in the oven. Bake for 15–20 minutes, or until the top is golden brown and the cheese is bubbly.