Scrapburgers

Got some leftovers? Make a scrapburger!

Scrapburgers are exactly what it says on the tin, except for they don't come in a tin. Big fat burgers made out of yesterday's leftovers. Mmmmmm, granny's favourite!
Ingredients vary on a daily basis, but onions, gravy and bread make a reliable base. Heavy seasoning is often required and many people use fragrant spices or hot sauces to mask the flavour.
The scrapburgers can be served with fresher ingredients like crisp salad leaves and a hefty portion of potato wedges, or it can be sliced up and shoved in a sandwich or wrap. The burgers can be quite messy depending on their ingredients, and loud, sloppy eating is frowned upon.
This dish is a common occurrence and is designed to reduce household food waste. It can be enjoyed* year round but is not generally served for any special occasions.
Many people cook this up for breakfast so that last night's supper scraps are as fresh as they can be. Scrapburgers are a well-known hangover cure when served with fried eggs and baked beans.
*flavours and quality may vary.

The best scrapburgers have a good balance of three important ingredients: sticky stuff, meaty stuff and tasty stuff.

— Granny's special recipe

Scrapburgers? Tastes-like-crap burgers more like!

— First time scrapburger maker

I used this prompt to get me started on this article:

What is a popular junk food in your world? Is the consumption of it generally frowned upon?