1. Set oven to broil.
2. Arrange salami and onions in a single layer on a baking sheet. Season with one tablespoon olive oil, salt, pepper, barbecue sauce, and garlic powder. Toss lightly to coat everything evenly.
3. Place in oven for seven to eight minutes. Remove tray from oven and flip the salami and onions. Place back in the oven for another five to seven minutes.
4. Change oven heat to 400 degrees Fahrenheit (200 degrees Celsius).
5. Arrange apple and sweet potato slices in a single layer on a baking sheet. Drizzle with remaining two tablespoons olive oil and maple syrup and toss to coat evenly. Season the sweet potato with salt, pepper, and garlic. Season the apples lightly with cinnamon, chili powder, and ginger.
6. Place in oven for 20 minutes. Remove baking sheet from oven and flip over. Return to oven for another five minutes. Remove apples from the oven. Roast the sweet potatoes for another 10 minutes.
7. To assemble, place a slice of salami on the bottom. Add a few slices of apple, a slice of sweet potato, and another piece of salami. Top with onions and stick in a toothpick to hold the “sandwich” together. Serve with whole-grain mustard on the side for dipping.