Vegetarian Reuben Sandwich

Name: Vegetarian Reuben Sandwich
Ingredients: 1 tablespoon extra-virgin olive oil; 1 small onion, thinly sliced; 1 clove garlic, thinly sliced; 1 pound bag sauerkraut, drained and rinsed; 1 sweet apple, peeled, and grated; Generous pinch allspice; Salt and freshly ground black pepper; 1/4 cup mayonnaise; 1 tablespoon chili sauce or ketchup; Dash hot sauce; 1 tablespoon minced fresh chives and/or fresh dill; 2 teaspoons capers, chopped; 1 teaspoon freshly squeezed lemon juice; 1 tablespoon extra-virgin olive oil, optional; 12 slices tempeh bacon, optional; 1 to 2 tablespoons unsalted butter, room temperature; 8 slices rye bread; 12 slices dill pickle; 2 cups grated Swiss cheese (8 ounces); Kosher salt and freshly ground black pepper