Chicken and Sausage Gumbo

Name: Chicken and Sausage Gumbo
Ingredients: 2/3 cup canola oil; 3/4 cup all-purpose flour; 1/4 cup whole-wheat flour; 1/4 cup finely chopped onion, plus 2 cups roughly chopped; 1 cup low-sodium chicken broth; 1 cup chopped celery; 1/2 cup chopped green bell pepper; 2 teaspoons cayenne pepper; 1 teaspoon garlic powder; Kosher salt and freshly ground black pepper; 1 pound smoked sausage, sliced; 8 ounces tasso ham or andouille sausage, diced; 1 1/4 pounds skinless, boneless chicken thighs, cut into 1-inch pieces; 3 to 4 scallions, chopped; Cooked white rice, for serving (optional)