Roast beef sandwich with lots of spinach.

That's a combination I've never thought of, and I'll bet it's delicious. 
I used fresh spinach instead of lettuce and it was very good.
Mother's Poboys in New Orleans has used cabbage leaves instead of lettuce for years on their sandwiches. It's not bad and always uses up the leftover cabbage we have around at times. Particularly good with roast beef and spicy mustard on rye bread.
* mind thinks horrible things, food-wise, reading the "... used cabbage leaves instead of lettuce for years ..." *
* probably isn't about 'mature' sauerkraut *