Halve the sweet potatoes lengthwise. Place cut side up on the baking sheet. Top each sweet potato half with 1 tablespoon of the butter. Sprinkle with the onion powder and caraway seeds. Bake for 45 minutes to 1 hour.
While the sweet potatoes are baking, heat a large skillet over medium heat. Heat the olive oil in the pan, then add the corned beef, sauerkraut and garlic. Sauté until heated through, about 10 minutes. Drain any excess liquid and lower the heat to low.
When the sweet potatoes are finished baking, fork rake the top of them to loosen their flesh.
Top each sweet potato with a heaping portion of the corned beef mixture. Top with a slice of Swiss cheese and drizzle with Russian dressing. Garnish with chopped green onion, if desired.
For the Russian Dressing
In a large mixing bowl, combine mayonnaise, ketchup, mustard, Worcestershire sauce, parsley, chives and dill. Mix until all ingredients are well incorporated.