Bring a large pot of salted water to a boil. Add linguine and cook until al dente, 9–11 minutes. Reserve ¼ cup of pasta water, then drain and toss with a little olive oil.
Combine garlic powder, onion powder, paprika, cayenne, salt, and pepper. Coat the cubed chicken evenly with the spice mix.
In a skillet, heat olive oil and 1 tablespoon of butter over medium-high heat. Sear chicken in a single layer for 3–4 minutes per side until golden and cooked through. Remove and cover with foil to keep warm.
Lower the heat to medium-low. Add remaining butter and minced garlic, cooking just until fragrant. Stir in chicken broth, lemon juice, and Dijon mustard. Simmer for 2 minutes.
Stir in heavy cream and Parmesan cheese. Mix gently until smooth and slightly thickened. Do not boil.
Return the chicken and linguine to the skillet. Toss well, adding a splash of reserved pasta water at a time until the sauce clings beautifully to the pasta.
Stir in parsley and garnish with extra pepper, red pepper flakes, or lemon wedges. Serve immediately for the best flavor and texture.
