In a nonstick frying pan, saute the onions over medium heat until they''re translucent, about 5 minutes. Add the beef and continue to cook for another 5 minutes or until the beef is tender and browned throughout. Drain well and set aside.
Fill a large pot 3/4 full with water and bring to a boil. Add the noodles and cook until al dente (tender), 10 to 12 minutes, or according to the package directions. Drain the pasta thoroughly.
In a saucepan, whisk together the soup, water and flour over medium heat. Stir until the sauce thickens, about 5 minutes.
Add the soup mixture and paprika to the beef in the frying pan. Over medium heat, stir the mixture until warmed through. Remove from heat and add the sour cream. Stir until combined.
To serve, divide the pasta among the plates. Top with the beef mixture and serve immediately.