Begin by combining all the russian dressing ingredients in a bowl. Mix together well and taste for seasoning, Adjust as necessary. Set aside.
To make the sandwich, first drizzle a small amount of oil in a skillet and heat the pastrami. The meat is cooked already, but still needs to be heated up. This takes a minute. When done, remove to a plate and set aside. Then heat up the sauerkraut for a few seconds until heated through. Set aside.
Butter 1 Tb on 1 side of bread and the other Tb of butter on the other piece of bread. In the same skillet, toast the bread, butter side down. Then spread on 1-2 TB of Russian dressing on 1 slice of bread, then add the pastrami, sauerkraut and cheese. Top the sandwich the 2nd slice of bread.
Cover pan with a lid so that the cheese can melt, about another minute.
When done, cut sandwich in half and serve with your favorite pickle.
Notes
The Russian dressing yields more servings, so save for another use!