Bring a large pot of salted water to a boil, then add the pasta and cook until just al dente, about 8-10 minutes. Drain and set aside.
Meanwhile, heat olive oil in a large sauté pan over medium heat. Add chopped onions and minced garlic, cooking until fragrant and translucent, about 5 minutes.
Add chopped mixed vegetables to the pan and sauté until tender and slightly caramelized, about 7-8 minutes. Stir occasionally to prevent sticking.
In a large bowl, combine the cooked pasta with the sautéed vegetables, then fold in the tomato sauce and dried oregano. Mix well to evenly coat everything.
Add half of the vegan cheese to the mixture and stir until melted and incorporated.
Transfer the mixture into a greased 9x13 inch baking dish, spreading it evenly with a spatula.
Sprinkle the remaining vegan cheese evenly over the top, creating a gooey, cheesy layer.
Bake uncovered in a preheated oven at 180°C (350°F) for 20-25 minutes, until bubbly and golden on top. Check at 20 minutes to prevent over-browning.
If the top browns too quickly, cover loosely with foil and continue baking. Once done, remove from the oven and let rest for 5-10 minutes.
Serve warm, garnished with fresh herbs if desired. Enjoy the bubbly, cheesy, and hearty vegan pasta bake!