Prepare the cornbread according to package directions, adding ½ cup of grated cheddar cheese to the batter before baking. Allow the cornbread to cool completely.
Crumble the cornbread into large pieces over a very large bowl.
Add the tomatoes, celery, bell pepper, onion, mayonnaise, and garlic salt to the bowl. Stir gently until completely combined. Cover and refrigerate for at least 2 hours (or up to 24 hours) until ready to serve.
Just before serving, top with crumbled bacon, additional cheese, and fresh chives.
