Tried quite a few ways and this is what I found best:
Slice your goose breasts 1/4" thick or as close to that as you can
Season with salt and pepper or whatever you like (or not)
I like to dunk the slices in teriaki sauce
Cook on a hot charcoal grill two minutes to a side and it's done.
It will taste like steak.
If you cook it too long it will taste like liver. It's better to be a little under-cooked than over-done and livery tasting.
Someone will top this recipe with one that's similar but with cheese and hot peppers stuffed inside