Pat dry the beef cubes and sprinkle with salt and pepper.
In a large skillet, heat the olive oil over medium high heat. Once very hot, add the beef cubes to the skillet and brown in two batches, about 5 minutes each batch, turning the cubes over halfway through. Place the beef cubes in the slow cooker.
To the same skillet, reduce heat to medium, add the diced onion and garlic and balsamic vinegar, cooking until onions have softened about 5 minutes. Add in the tomato paste and cook for just another minute, then add this mixture to the slow cooker.
Add the carrots, potatoes, celery to the slow cooker. Crumble the beef bouillon cubes on top of the vegetables and add the hot water. Add the dried parsley, dried herbs, thyme or oregano, and paprika. Stir the ingredients in the slow cooker to evenly distribute.
Cook on low heat for 7-8 hours or high heat for 3-4 hours. Once beef cubes are tender and can easily be cut apart with a fork, it's ready. To thicken the stew, remove a few tablespoons of the liquid from the slow cooker to a small bowl, add the cornstarch and mix until a paste forms, then return the cornstarch paste to the bowl of the slow cooker. Cook for another 10-20 minutes.