Pre-heat the oven to gas mark 6 (200°C). Arrange the shelves towards the mid-top area of the oven; x3 dishes will need fit. Prepare all ingredients according to their instructions.
Add the peeled baby onions to an oven-friendly pan, (a cast iron shallow casserole dish or frying pan works really well here) then pour over the olive oil and mix in the sugar. Pop into the oven to roast for around 30 minutes; check and turn occasionally whilst they cook.
Place the prepared butternut squash into a small bowl with the minced garlic, fresh thyme, black pepper and olive oil and toss to combine the flavours. Lay two sheets of foil on a work surface and divide the butternut squash mix between the two. Fold into parcels, sealing tightly. Place into the oven alongside the onions and roast for 30 minutes.
Pour the groundnut oil into an oven-friendly frying pan and heat through. Add the trimmed and halved pork tenderloins to the pan and rotate to nicely brown all sides, sealing the meat. This should take about 3-5 minutes. Remove the pork tenderloins and brush all over with the mustard. Pour the dukkah spice mix onto a plate and sprinkle over the back pepper. Roll each tenderloin in the spice mix to generously coat and place back into the frying pan. Pop the pan, uncovered, into the oven and cook for around 15-18 minutes (as a guide this is approx. 5 minutes per 100g). Rotate the pork halfway through cooking.
Whilst the cabbage is cooking, tip the butternut squash into a bowl and add the butter. Mash until smooth and season to taste. Remove the baby onions from the oven, loosening with a splash of water if sticky. Everything should now be ready to plate up.
To serve, slice the pork tenderloin into even pieces, reserving the resting juices to pour over the top (if you have any onion water, mix this into the resting juices for extra flavour). Place the mash onto warmed plates alongside the savoy cabbage and baby onions, lay the pork across the top and pour over the resting juices.