Heat a large sauté pan over medium heat and melt butter and olive oil together. Add onions and season with salt and pepper. Reduce heat to a low simmer, stirring occasionally and cook until onions have caramelized (about 40-60 min). Set aside to cool.

Preheat oven to 400°F

Roll out the pie crusts onto a greased, parchment paper lined baking sheet. Spread hummus and Dijon mustard on crust leaving about a half-inch border around the edge of the pie crust. Scatter the caramelized onions on top of the hummus and cover with the sliced zucchini, tomatoes, mozzarella, and feta cheese. Sprinkle your fresh thyme over the top and drizzle some olive oil over everything. Finish it off with some salt and pepper to taste.

Fold in the edges of the pie crust and brush with your beaten egg. Bake for about 15 minutes or until the crust is golden brown and vegetables have softened.

Slice and serve warm (these reheat really well too!)