Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius).

Sauté onion in olive oil until soft and lightly golden. Add the diced pastrami, sauté for a few more minutes until warmed through, and season lightly with salt and pepper. Remove from heat and allow to cool.

Grate the carrot, onion, and celery in a food processor. Transfer to a bowl and mix well with the remaining ingredients until fully combined. Fold in the cooled pastrami mixture.

Spray 10 3-inch (7 and 1/2-centimeter) round aluminum pans with cooking spray. Divide the kishka-pastrami mixture evenly among the pans. Lightly spray the tops. Bake for 20 minutes, then remove from oven and allow to cool.

Preheat grill and combine all the ingredients for the maple Dijon glaze in a small bowl.

Whisk together rice vinegar, lemon juice, olive oil, honey, Dijon mustard, salt, and freshly ground black pepper. Toss with cabbage and let it sit briefly so it softens and absorbs the flavor.

When ready to serve, baste kishka rounds with the glaze and grill for three to four minutes per side, brushing again with the glaze after flipping.

Spread maple Dijon glaze on a pretzel slider bun. Add a grilled kishka round, drizzle with more sauce, top with a heaping spoonful of slaw, and finish with pickled red onions. Repeat with remaining slider buns. Serve warm.