Heat a drizzle of oil in a skillet set over medium-high heat and brown the beef in batches, sprinkling with salt and pepper.
As the meat browns, transfer it to the bowl of a slow cooker. (If you want to skip this step, toss the meat directly into the slow cooker.)
Cook the onion in the pan, scraping the bottom to loosen any browned bits, and put them in the slow cooker along with the beef.
Add the stock and Pickapeppa sauce, cover and cook on low for 5-6 hours, then stir in the stew mix and cook for another hour, or until the vegetables are just tender.