Heat oil in large heavy based casserole dish over medium heat. Cook beef in batches for 5 - 6 minutes or until browned. Transfer to a bowl.
Return beef to pan. Add carrots and vinegar. Cook stirring for 2 minutes or until the vinegar is reduced slightly Stir in soup and stock. Cover. Bring to boil. Reduce heat to low. Simmer for 2 hours or until beef is tender. Season with salt and pepper to taste.
Meanwhile cook the lentils according to packet directions. Drain. Add to beef mixture. Season with salt and pepper. Stir to combine.
Note: You could use a 400gm can of lentils, draioned and rinsed instead of dried lentils.