Roast the butternut squash cubes, tossed in approx 1 tablespoon olive oil, at 400F for 30-40 minutes until tender and just starting to brown. This can either be done ahead or alongside the rest of the meal - just allow the squash to cook around 20mins before starting the rest.
Heat remaining ½ tablespoon oil and butter over medium heat. Soften onion 2-3 mins, add garlic, cook another 2-3 mins until onion starting to brown.
Add rice and cook briefly to ensure well coated in oil/butter mixture.
Add wine, stir and cook until all the liquid is absorbed.
Add stock a bit at a time (around ½ to 1 cup at a time), adding more as the last is absorbed. Stir now and again as it cooks - I generally only stir as liquid is absorbed initially but then a little more towards the end when it tends to stick to the bottom more. In all it takes around 20mins.
Meanwhile mash around ½ cup of the cooked squash.
Once all the stock is absorbed, check rice is cooked (if not then add a little more stock) then add arugula and stir in so it wilts.
Add parmesan and mashed squash and stir well.
Add chicken and remaining squash, stir and serve.