Bring a large pot of salted water to a boil and cook the penne pasta according to package instructions until al dente. Drain and set aside.
In a large skillet, heat the olive oil over medium heat. Add the chopped red onion and minced garlic, sauté until the onion is translucent, about 3-4 minutes.
Add the diced zucchini and bell pepper to the skillet, cook for another 5 minutes until they begin to soften.
Stir in the halved cherry tomatoes, chopped spinach, oregano, and basil. Cook for an additional 3-4 minutes until the spinach wilts and the tomatoes start to soften. Season with salt and pepper to taste.
In a large mixing bowl, combine the cooked penne pasta with the sautéed vegetable mixture. Add the crumbled feta and black olives (if using), then toss gently until well combined.
Transfer the pasta and vegetable mixture into a greased baking dish. Sprinkle the shredded mozzarella cheese on top.
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it cool for a few minutes. Garnish with fresh basil leaves before serving.
Notes
Serve the pasta bake in individual portions, garnished with extra feta and fresh basil on top for an added touch of color and flavor.