Make up some simple tuna salad - tuna, mayo, mustard, minced onions, pickle relish, salt and pepper (no celery because I don't have any) and a bit of tart apple (why apple? see previous shortage).
How much of each you say... go by taste. Start with a little and add until it seems right.
Spread over the Rosemary bread, drape a slice of cheddar cheese over it and TOAST!
I recommend a dry white wine or a fruity red. Really - wine with Tuna salad elevates the whole endeavor. And it is Friday. So eat greek olives while you are preparing this and sipping wine. Or don't use apples and relish and put in olives instead. Hmmmmm.
Have a yummy weekend.