The thing to remember about tarts, galettes and the like is that there are no rules. They're really just open-faced pies.
Simply take a bunch of flavors you like (that you think will go together), chop them up, and sprinkle them about. Here's what I did:

* Preheat your oven to 450, and bake a sheet of it on a (greased) cookie pan for ten minutes.
* While it's pre-baking, gather and chop your fillings.
I chose:
Carmelized Red Onions
Tri-tip (leftover from the night before)
Tomatoes (salted and peppered)
Chopped Green Onions
Crumbled Bleu Cheese
* Sprinkle your fillings evenly over the pre-baked sheet of puff pastry.
* Take another (raw) sheet of puff pastry and cut it into whatever shapes suit your fancy and place them on top.
* Bake for another ten minutes. Slice and serve!