Just happened to have these ingredients in my house at the time...not quite a real Reuben, and no sauerkraut involved, but was the BOMB and made me feel like I had created a gourmet sandwich. ha

Butter two slices of light Rye bread, one side only
Dijon mustard on the unbuttered sides of the bread
Pastrami - pile it up
Few slices of Brie cheese (I used an herbed one)

Medium to Med-high pan (I used a cast-iron skillet), put the sandwich together and cook both buttered sides until bread is golden brown and the brie is melted. The taste speaks for itself (at least it spoke to me at the time!).