Preheat the oven to 200C/390F. On a large baking tray, toss the broccoli with a drizzle of olive oil and a good pinch of salt and pepper. Bake in the oven for 15 minutes, or until it begins to lightly char and soften.
In a large pan over medium heat add the bacon. Fry until crisp with the fat rendered down, then remove and place to one side. Increase the heat to medium-high and add the chicken to the leftover fat. Season the chicken with ¼ tsp salt and pepper, then fry until it builds up a golden crust and is just about cooked through. Remove and place to one side.
Lower the heat back down to medium and melt in the butter. Stir in the flour to create a roux then gradually add in the milk and stock, whisking as you go to prevent lumps. Stir in the mustard, chives, nutmeg and pepper. Bring to a gentle bubble, then turn off the heat and stir through the cheese. Once melted, stir through the broccoli, chicken and bacon. Pour into a baking dish and leave to cool for 10 minutes.
Slice the bagels in half, then slice into chips around ¼" thick. Neatly layer them over the filling. Liberally spray with oil then place in the oven for around 20 minutes, or until the bagel chips are deep golden and crispy with the filling bubbling around the edges. Rest for a couple of minutes then serve.
