1. Prep ingredients
Preheat the oven to 220C, fan-forced. Bring a medium saucepan of salted water to the boil for the spaghetti. Cut the onion into thin wedges. Coarsely chop the parsley leaves and finely chop the stems.
2. Bake feta and veggies
Put the piece of feta in the centre of a 1L (4 cup) baking dish, then add the tomatoes, onion, parsley stems and unpeeled garlic cloves. Drizzle with 1½ tbs olive oil, scatter over the Italian seasoning and season with salt and pepper. Toss the veggies to combine and turn the feta to coat. Bake for 20-25 mins until the onion is soft.
3. Cook spaghetti
Meanwhile, cook three-quarters of the spaghetti* in the pan of boiling water for 12 mins or until al dente. Reserve 80ml (⅓ cup) cooking water, then drain the spaghetti.
4. Make sauce
Squeeze the garlic flesh from the skins, then mash with a fork. Add the garlic and reserved cooking water to the roasted veggies and feta. Mash with a fork until well combined (the feta will be a little grainy). Add the spaghetti and toss to coat. Taste, then season with salt and pepper.
5. Serve up
Put 2 tsp olive oil and 1 tbs balsamic vinegar in a large bowl, season with salt and pepper and whisk to combine. Add the spinach and toss to coat. Divide the baked feta spaghetti among bowls and scatter over the parsley leaves. Serve with the dressed spinach and enjoy!
6. Make it yours
If you like a kick of heat, add a pinch of chilli flakes to the sauce, or scatter over to serve if it's just for you.