Between the buns, there is crispy bacon, melted cheese, a thick patty, a sliced tomato, lettuce and maybe mayonnaise.

Hi Elisa -

Grammatically there is very little wrong with what you wrote and in terms of sounding natural you've done a very good job as well.  The most obvious grammatical error is "....there are crispy bacon...".  It should be:  "...there IS crispy bacon....".  Here is how I might tweak it to sound a little more natural:

I'm going to try to describe the picture below.

I would be grateful for any suggestions that might make it sound more natural.

********

This is a picture of a hamburger. Between the buns, there is: crispy bacon, melted cheese, a thick patty, a sliced tomato, lettuce and maybe mayonnaise. I love cheese on all kinds of other food as well, so the melty* cheese looks very appetizing and makes me hungry.
The only thing I’m concerned about is that it looks so big that I may not be able to bite into it!!
*******
Thanks for reading my notebook.

* I think 'melty' is kind of an informal word, but one that you would expect to hear in advertising, so I think it sounds good here. 

Nice job :)

Picture Description: ‘Hamburger'

Great job, Elisa!  I hope that helps...now, I really want a hamburger, lol! - Stacy