Put the onion, beetroot, carrot, potatoes, garlic, and herbs into a roasting tray and season them well with salt and pepper and add olive oil. Mix well so that all the vegetables are covered in oil. (Add a little more if necessary).
Place into the oven and cook for approx 40-50 mins, stirring once halfway through cooking. The spinach will need to be added to these vegetables 5 mins from completion of cooking time.
When the vegetables have been in the oven for 20 minutes, start cooking the Gressingham duck breasts. Place an empty roasting tray in to the oven to keep it warm.
Take the breasts and lightly score the skin and pat dry. Place the breasts skin side down in a frying pan on a low to medium heat with no oil. Cook for 6-8 minutes until the skin is golden and crispy. Be sure to carefully pour off any excess fat as it is cooking.
Once the skin is crispy, flip the duck over and sear the meat for 30 seconds. Transfer to the warm baking tray and place in the oven to cook for 12 mins for a medium rare result (leave in the oven for longer if you like your duck well done.)
Remove from the oven and allow to rest until the vegetables are cooked.
Once the spinach has been added and cooked through, remove from the oven, pour over the balsamic syrup, mix well with the vegetables and serve onto 2 plates. Carve the duck and place on top of the vegetables.