Preheat the oven to 375°F (190°C).
Heat olive oil in a pan over medium heat. Add chopped onion and cook until translucent.
Add minced garlic and cook for another minute.
Add mixed vegetables, dried oregano, salt, and black pepper. Cook for 5-7 minutes until vegetables are tender.
Brush a baking dish with melted vegan butter. Layer 3-4 sheets of filo pastry, brushing each layer with melted butter.
Spread the vegetable mixture evenly over the filo layers.
Top with another 3-4 layers of filo pastry, brushing each layer with melted butter.
Bake in the preheated oven for 30-35 minutes, until golden and crispy.
Let it cool for a few minutes before slicing and serving.