Dice 1 onion half; set aside.
Cut remaining onion half into slices. Place onion slices and bell pepper halves, cut sides down, on a baking sheet lined with nonstick aluminum foil; drizzle with oil, and sprinkle with salt.
Broil 5 inches from heat about 10 minutes or until bell pepper looks blistered. Place bell pepper halves in a zip-top freezer bag; seal and let stand 10 minutes to loosen skin. Peel bell pepper halves, and dice one half. Reserve diced bell pepper and remaining half. Dice roasted onion, and set aside.
Melt butter in a large skillet over medium-high heat. Add reserved diced raw onion, and sauté 10 minutes or until onion begins to brown. Stir in flour; cook, stirring constantly, 5 minutes, or until flour mixture is caramel-colored. Stir in chicken broth and Creole seasoning. Reduce heat to medium, and cook, stirring constantly, until thickened.
Process gravy mixture and reserved bell pepper half in a blender until smooth, stopping to scrape down sides.
Combine gravy mixture, reserved diced roasted bell pepper, diced roasted onion, basil, and black pepper.