Heat oven to 200C/180C fan/gas 6. In a small roasting tin, toss the rhubarb, onion wedges and garlic with the balsamic vinegar, a little olive oil and some seasoning. Roast in the oven for 20 mins.
Meanwhile, melt the butter over a high heat and fry the rosemary. Add the pork and cook for 2 mins on each side until nicely browned, then remove from the heat. Take the roasting tin out of the oven and add the grains and chicken stock and mix together. Add the meat and the rosemary to the roasting tin, placing the chops on top. Roast for 10-12 mins further, or until the pork is cooked through. Serve each chop with a big spoonful of the grains, scattered with parsley.