Reduce heat to medium and add the remaining 1 1/2 teaspoons oil to the pan. Add onions and cook, stirring, until softened, about 5 minutes. Season with salt and pepper. Add garlic and paprika; cook, stirring, until fragrant, about 1 minute more. Add flour and cook, stirring, for 1 minute. Add broth and bring to a simmer, stirring constantly. Stir in bell pepper. Cover and cook, stirring occasionally, until the peppers are softened and the sauce is slightly thickened, 4 to 5 minutes. Add the reserved chicken and cook, uncovered, until heated through, 1 to 2 minutes.