01 - Set oven to 400°F (200°C) and allow it to fully preheat.
02 - Add cherry tomatoes, sun-dried tomatoes, garlic, and 2 tablespoons olive oil to a large ovenproof baking dish. Season generously with salt, black pepper, dried oregano, and crushed red pepper flakes if desired. Toss thoroughly to coat.
03 - Place the feta cheese block in the center of the baking dish amidst the tomato mixture. Drizzle 1 tablespoon olive oil over the cheese and season lightly with black pepper.
04 - Transfer the baking dish to the oven and bake for 25 to 30 minutes until tomatoes burst and feta softens with golden edges.
05 - While the dish bakes, heat 1 tablespoon olive oil in a large skillet over medium heat. Add sliced onions and cook, stirring occasionally, for 15 to 20 minutes until deeply caramelised and golden brown. Set aside.
06 - Simultaneously, boil pasta in well-salted water according to package instructions until al dente. Reserve 1/2 cup pasta water and drain thoroughly.
07 - Remove baking dish from oven. Stir in caramelised onions and chopped basil, breaking the feta apart and blending ingredients to create a creamy sauce.
08 - Add drained pasta to the baking dish and toss gently to coat evenly. Splash in reserved pasta water incrementally for optimal sauce consistency.
09 - Plate immediately. Garnish with extra basil and a drizzle of olive oil if desired.