In a large bowl, combine the chicken, 3/4 teaspoon salt, 1/2 teaspoon black pepper, garlic powder, onion powder, and cayenne pepper until evenly combined. Set aside.
Preheat a large skillet over medium high heat. Once hot, add the bacon and cook, stirring often, until browned and crispy, about 5 to 8 minutes. Using a slotted spoon, transfer the bacon to a plate lined with paper towels. Carefully drain off the bacon grease and return to the skillet to the stove.
Add in 2 tablespoons butter, once melted, add in the chicken and cook until browned on both sides, about 5 to 8 minutes. Transfer to a cutting board and allow to cool slightly before dicing. Add the onion and garlic to the same skillet and cook until translucent, about 3 minutes.
Preheat oven to 375 degrees F. Grease a 9x13-inch casserole dish and set aside.
Add 2 more tablespoons of butter to skillet and stir until melted. Stir in the flour and cook for about 30 seconds, before whisking is the chicken stock and milk. Cook, stirring often, until the sauce has thickened. Remove from the heat and stir in the remaining salt, pepper, cream cheese, 1 cup Cheddar, and 1 cup Monterey Jack until smooth and melted through.
Add the chicken, pasta, half of the crispy bacon and pickled jalapeños and stir until well combined. Pour into the prepared baking dish and top with the remaining cheeses and bread crumbs.
Melt the remaining 2 tablespoons butter and drizzle over the top of the casserole. Bake until bubbly and golden brown, about 18 to 20 minutes. Remove from the oven and top with sliced the remaining bacon, jalapeño and scallions before serving.