Best Sandwich I have had in a while

In my quest for more simple and healthy dinners, I ran across a recipe for a Ruben sandwich that replaces the pastrami with spinach. Combined with quality rye bread, good swiss cheese and some sauerkraut, this sandwich has so much flavor going on, that you don't miss the fatty but tasty pastrami. The original recipe in Eating Well, calls for low fat cheese, and less of it, but this is a Ruben without pastrami, so live a little. I would double, triple or quadruple the dressing and save some for later.

Spinach Ruben Sandwich

Russian dressing
1/8 Cup reduced-fat mayonnaise
2 teaspoons ketchup
2 teaspoons chopped capers
1 teaspoon chopped pickle or relish

Sandwiches
3 teaspoons extra-virgin olive oil, divided
1 small red onion, thinly sliced or 3 shallots finely diced
1 cup sliced mushrooms
1 bunch spinach, cleaned and stemmed
Freshly ground pepper to taste
Pinch of nutmeg, freshly ground
4 slices rye bread
4 thin slices Swiss cheese
1/2 cup sauerkraut

1. To prepare Russian dressing: Whisk mayonnaise and ketchup in a small bowl until smooth. Stir in capers and pickle (or relish).
2. To prepare sandwiches: Heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Add onion or shallots and mushrooms; cook, stirring often, until the onion is softened, 4 minutes. Add spinach and cook, stirring, until it has wilted, 1 to 2 minutes. Add salt, pepper and nutmeg to taste. Transfer the mixture to a plate.
3. Coat the pan with the remaining 1 teaspoon oil and return to medium heat. Add the bread; divide cheese equally among the slices. Divide sauerkraut between 2 slices and divide the spinach mixture between the other 2 slices; cook until the cheese has melted and the bread is golden brown, 4 to 6 minutes. Transfer sandwich halves to a cutting board. Divide the dressing between the spinach halves. Carefully place the sauerkraut halves on top. Cut sandwiches in half and serve.