I've never made this in a crockpot, but it would probably work. This is my mother's recipe, and was a huge favorite in our family. She normally baked in the oven, but I think it would work in a crockpot. Very simple to make.

Swiss Steak
London broil
salt
pepper
1 large onion, sliced
2 cans chopped tomatoes
Yellow mustard

I will salt and pepper the London broil. (Sometimes I dredge in a little flour and then brown in a little olive oil, but not sure if you really need to do this).

Place London broil in crockpot and then layer sliced onions on top. Squeeze yellow mustard on top (you use a lot, maybe 1/4 cup?). Pour the canned tomatoes on top. Do not mix around!

Then cook (for however long you're supposed to cook in a crockpot).

Marilyn