In a large saucepan, melt the butter with the paprika over medium heat. Add the onion and cook, stirring, for 3 minutes. Sprinkle in the flour and cook, stirring, for 2 minutes. Stir in the tomatoes. Cook, stirring, until the mixture begins to simmer and thicken, about 2 minutes. Stir in the bell pepper and broth. Cover and simmer over medium heat, stirring occasionally, until the pepper is tender, 15 to 20 minutes.
Add the chicken and cook just to heat through. Stir in the sour cream, 1/4 cup at a time; season with salt and pepper. Top with the parsley before serving.