Heat olive oil in a large skillet set over medium heat.
Meanwhile, combine chili powder, paprika, cumin, salt, and pepper in a small dish.
Season tilapia fillets with the prepared spice rub.
Add tilapia to the hot oil and cook for 3 minutes per side, or until cooked through; remove from skillet and keep covered. Cooking time will depend on the thickness of the fillets.
Set skillet back over medium heat and melt the butter.
To the butter, add the diced onion and cook for 3 to 4 minutes, or until softened.
Stir in garlic and cook for 20 seconds, or until fragrant.
Whisk in heavy cream, chicken broth, and tomato sauce; whisk until smooth.
Season with Italian seasoning and bring mixture to a slow boil.
Lower heat to a steady simmer and continue to cook for 8 minutes. Whisk occasionally.
Taste sauce for salt and pepper; adjust accordingly.
Return fish to the skillet and continue to cook for 2 more minutes, or until heated through.
Remove from heat.
Garnish with parsley.
Serve.