Preheat your oven to 375°F. Grab a baking dish—no need to be fancy.
Cook the pasta according to package instructions. Don’t overdo it—it’ll keep cooking in the oven.
In a large bowl, toss the cooked pasta with olive oil, onion, garlic, oregano, salt, pepper, diced tomatoes, olives, and sun-dried tomatoes.
Pour everything into your baking dish. Sprinkle feta and mozzarella over the top like you’re feeling generous (because you are).
Bake uncovered for about 20-25 minutes, or until everything’s bubbly and golden and your kitchen smells like a Greek grandma’s hug.
Top with fresh parsley, if you're feeling extra. Serve hot, ideally with a napkin under your chin.