Place the pitas on a baking sheet and brush each pita with olive oil.
Arrange pear slices over the top in a single layer, followed by onion slivers, blue cheese crumbles, and lastly the walnuts.
Place the baking sheet into the oven and bake for 10-15 minutes, until the pitas are brown, the pears are soft and golden, and the cheese has melted slightly.
If needed, finish the pita pizzas under the broiler for 1-2 minutes, watching them very carefully.
Remove from the oven and let the pita pizzas cool for 2 minutes, then slice into quarters and serve immediately.