1. Cook Fettuccine according to the package instructions.
2. Meanwhile heat olive oil in a pan. Add onions, garlic and saute for few min.
3. Add in butter. Add sliced vegetables. Add salt, pepper and Italian seasoning.
4. Cook until vegetables are tender. Stir in the Tomato sauce.
5. Bring to a boil. Add cooked pasta, tomatoes and spinach.
6. Combine all together. Add mozzarella, Parmesan and red chili flakes.
7. Mix everything gently and add crumbled feta cheese just before turning off the heat.