Combine the shredded chicken with 1 cup BBQ sauce in a medium bowl and mix until well combined.
Arrange a layer of half of the tortilla chips on a large baking sheet or oven-safe dish. Top the chips with half of the shredded chicken mixture.
Sprinkle half the cheese, half the diced red onion, and half the sliced pickled jalapeños over the chicken and chips.
Repeat the layers with the remaining tortilla chips, shredded chicken, cheese, red onion, and jalapeños. Drizzle over the remaining 1 cup BBQ sauce.
Place the baking sheet or dish in the preheated oven and bake for about 10-12 minutes, or until the cheese has melted and the nachos are heated through.
Remove from the oven and garnish with chopped cilantro, fresh tomato salsa, and guacamole (if using). Allow the nachos to cool for a few minutes before serving.
Serve the BBQ chicken nachos while they're still warm with any additional toppings if desired.