Preheat your oven to 400°F (200°C). Roll out your pie crust on a lightly floured surface until it's large enough for a 9-inch pie dish. Press the crust into the dish and brush with melted butter.

Heat olive oil in a large skillet over medium heat. Sauté diced onion and minced garlic for 1-2 minutes. Mix in chopped carrots, celery, zucchini, mushrooms, and peas. Cook for 5-6 minutes.

Sprinkle all-purpose flour over the vegetables, stirring to coat. Gradually whisk in milk until smooth. Add thyme, rosemary, salt, and pepper, and simmer for about 3 minutes.

Pour the vegetable sauce into the prepared pie crust. Cover with a second crust, seal edges, and cut slits for steam to escape. Bake for 25-30 minutes until golden.

Remove from oven and let cool for 5-10 minutes before serving.