On a plate, combine the flour with salt and pepper.
Dredge each chicken breast in the flour mixture, coating both sides, then set aside.
Bring a large pot of salted water to a boil and cook the linguine according to the package instructions; drain and keep warm.
Heat the olive oil and butter in a large skillet over medium heat until the butter is melted and sizzling.
Fry the dredged chicken breasts for about 3–4 minutes per side, until golden; remove from the skillet and set aside.
Add the minced garlic and onion powder to the skillet and cook briefly until fragrant, about 30 seconds.
Pour in the chicken stock and simmer for 2–3 minutes, scraping up any browned bits from the pan.
Add the crushed tomatoes and sugar, season with salt and pepper to taste, then reduce heat to low and simmer the sauce for 25–30 minutes.
With about 5 minutes remaining in the sauce's simmer time, stir in the chopped parsley.
Return the fried chicken breasts to the skillet, top each with grated Parmesan, cover, and cook until the cheese is bubbling and the chicken is cooked through, about 3–5 minutes.
Serve by placing linguine on plates, spooning sauce over the noodles, and topping each with a chicken breast; garnish with additional parsley and Parmesan if desired.