The story...is recalled by the adult Scout; this allows her first-person narrative to contain adult language and adult insights yet still maintain the innocent outlook of a child.

Depending on how much detail you would like to include in a drawing, you might depict Scout as an older person writing this book and find a way to show the action or events of the book in the picture. 

A thought bubble might be partitioned into sections like a comic strip or comic book, with various events depicted within each section. This way, the six year old Scout can be included along with the adult Scout.

Scout Finch, who narrates in the first person ("I"), is nearly six years old when the novel opens.

The attack at the end of the novel with Scout in her ham costume is a visual scene that should be easy to draw. The letter delivered via fishing pole is also rather visual, as is the scene where Scout rolls into the Radley yard inside a tire. 

Any of these scenes can be drawn in a thought bubble while the older Scout, the omniscient narrator, is pictured writing or typing the narrative. This method demonstrates the idea that Scout is both in and out of the story, as the first person narrator removed from the events by intervening years.