Preheat the oven to 375ºF (190ºC). Line a baking sheet with parchment paper to prevent the sliders from sticking.
In a skillet, add oil, sliced red onions, and a pinch of salt. Cook gently for 10 to 15 minutes, stirring occasionally, until tender and golden. Set aside.
Slice the brioche buns in half. Generously spread Thousand Island dressing on the inner sides of both halves.
Place a slice of Swiss cheese on the bottom half of each bun.
Add a portion of smoked meat, the caramelized onions, a spoonful of sauerkraut, and another slice of Swiss cheese.
Close the sliders with the top bun.
Arrange the sliders on the baking sheet and press them gently with a spatula to seal them well.
Bake for 10 to 12 minutes, or until the buns are golden and crispy and the cheese is melted (you may need to cover you sliders with aluminium foil fpr the last 6 minutes to prevent burning).
