Preheat oven to 400 degrees. Butter an 8 by 8-inch baking dish or a 9-inch deep dish pie dish, set aside.
In a small mixing bowl, combine drained diced tomatoes, chopped olives, 1 Tbsp fresh basil and dried oregano, set aside. Boil pasta to al dente according to directions listed on package.
Drain pasta well and return to pot. Meanwhile, melt butter along with olive oil in a medium saucepan over medium heat. Add onion and saute until soft and lightly golden, about 3 - 4 minutes, adding in garlic during the last minute of sauteing.
Whisk in flour, and cook stirring constantly for 1 minute. While whisking vigorously, slowly pour in milk and bring mixture just to a boil, stirring constantly.
Once mixture reaches a boil reduce heat to medium-low and simmer, stirring constantly until mixture has thickened, about 3 minutes. Remove from heat, stir in 2 oz feta cheese and mozzarella cheese then season with salt and pepper to taste.
Pour tomato mixture over well drained pasta in pot and toss, then pour sauce over pasta mixture and toss to evenly coat. Pour coated pasta mixture into prepared baking dish.
Sprinkle top evenly with remaining 4 oz crumbled feta cheese. Bake in preheated oven 20 - 25 minutes until edges are bubbling and top is golden brown.
Serve warm garnished with fresh basil ribbons if desired.