Bring a large pot of salted water to a boil and cook spaghetti according to package instructions until al dente. Drain and set aside.
Heat olive oil in a large skillet over medium heat. Sauté chopped onion until soft, about 3 to 4 minutes.
Add minced garlic to the skillet and cook for 1 more minute.
Add ground beef and cook until browned, breaking up large pieces.
Stir in tomato sauce, Italian seasoning, salt, pepper, and red pepper flakes if using. Simmer gently.
Pat catfish fillets dry. In a shallow bowl, combine flour, cornmeal (if using), paprika, salt, and pepper.
Dredge each catfish fillet in the flour mixture, shaking off excess.
Heat oil in a skillet over medium-high heat. Fry catfish fillets until golden and crispy, about 3 to 4 minutes per side.
Transfer fried catfish to paper towels to drain excess oil.
Plate cooked spaghetti and top with beef sauce. Serve crispy catfish alongside or on top, garnished with parsley or Parmesan if desired.