Heat the oil in a skillet over medium heat. Add the beef chunks and brown on all sides for about 5 minutes. Transfer the beef to the slow cooker.
Add the diced onion, garlic, and ginger to the same skillet. Cook for 3 minutes until the onion softens. Scrape everything into the slow cooker.
Stir the vinegar, diced tomatoes, paprika, cayenne, cumin, coriander, turmeric, and salt into the slow cooker. Mix well to coat the beef.
Cover and cook on low for 8 hours until the beef is fork-tender.
About 30 minutes before serving, rinse the basmati rice and cook it in a medium pot according to package directions.
Warm the naan bread in a dry skillet or low oven for 2 minutes per side.