If using the oven, heat oven to 350°F.
Heat oil over medium-high heat in a large skillet (OR in a large oven-safe pot - like a Dutch oven). Brown beef for a couple of minutes on all sides, sprinkling with salt and pepper as it cooks. Transfer to a 5-6 quart slow cooker (OR set aside on a plate).
Add onion and garlic to the pan and cook for 2 minutes. Stir in Italian seasoning and tomato paste, then stir in 1/2 cup beef broth and the soy sauce. Scrape any browned bits off the bottom of the pan, then transfer to the slow cooker (OR add the meat back into the Dutch oven).
Add all vegetables EXCEPT for the peas, then pour over the remaining 2 cups of broth.
Cook on LOW for 6-8 hours or on HIGH for 3-4 hours. (Cook 2 hours in the oven, stirring CAREFULLY (HOT!) every 30 minutes; lower heat to 320°F if ingredients on top start browning too fast); do not stir in slow cooker!).
Open the lid, stir, then add the peas. Cook without the lid for 15 more minutes (OR 5 minutes on the stove).
To thicken, stir glucomannan into a few tablespoons of cold water in a small bowl. Add to the stew, 1/3 at a time, stirring well after each addition. The stew will thicken after 1-3 minutes. Only add enough glucomannan until the stew has thickened to your liking! Then serve immediately.