Dice 1 onion half, set aside.
Cut remaining onion half into slices. Place onion slices and bell pepper, cut sides down, on baking sheet lined with non-stick aluminum foil; drizzle with oil, and sprinkle with salt.
Broil onion slices and bell pepper halves 5 inches from heat about 10 minutes or until bell pepper looks blistered. Place bell pepper halves in a freezer bag; seal and let stand 10 minutes to loosen skin. Peel bell pepper halves, finely chop 1 bell pepper half. Reserve and set aside chopped bell pepper and remaining bell pepper half. Finely chop onion slices, and set aside.
Melt butter in a large skillet over medium-high heat. Add reserved diced onion, and sauté 10 minutes or until onion begins to brown. Stir in flour; cook; stirring constantly, until flour mixture is caramel-colored (about 5 minutes). 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 finely chopped bell pepper and onion, basil, and black pepper.