Bring a large pot of salted water to a boil and cook the pasta until al dente, about 8-10 minutes. Drain and set aside.
While the pasta cooks, heat olive oil in a skillet over medium heat. Add the chopped onion and sauté until translucent and fragrant, about 5 minutes.
Add the minced garlic to the skillet and cook for another minute, until fragrant, stirring constantly.
Stir in your mixed vegetables and cook until they soften slightly, about 3-5 minutes. Season with salt and pepper to taste.
In a large mixing bowl, combine the cooked pasta, sautéed vegetables, and tomato sauce. Mix well to coat everything evenly.
Stir in your vegan cheese or nutritional yeast to add cheesy flavor and creaminess, adjusting seasoning as needed.
Transfer the mixture into a greased baking dish, spreading it out evenly.
Top the casserole with breadcrumbs for crunch, or sprinkle more vegan cheese if desired.
Bake in a preheated oven at 180°C (350°F) for 25-30 minutes, covered with foil for the first 20 minutes. Remove the foil for the last 5 minutes to brown the top.
Once baked, let the dish rest for 5 minutes out of the oven to allow the sauce to set. Garnish with fresh herbs if desired and serve warm.