In a large, heavy skillet, heat the olive oil over high heat. Season each side of the chuck roast with the salt and pepper, then sear in the hot skillet for 3-5 minutes per side. In a large slow cooker, place the sliced onion on the bottom of the crock and then place the seared beef on top.
In the same heavy skillet, add in the beef broth and scrape up any bits on the bottom of the pan. Stir in soy sauce and tomato paste and whisk together. Pour the sauce over the beef adding in a ½ cup of water.
Wrap the potatoes, butter and ½ teaspoon of salt in an aluminum foil packet. Poke a few holes in the top and then nestle on top of the beef in the slow cooker. Place the lid on the slow cooker and cook on HIGH for 6 - 8 hours or until the meat is fork tender.
In the still hot skillet, add the peppers to the pan, adding in a teaspoon of oil if needed. Cook for 5 minutes or just until peppers start to soften. Transfer to a dish and store in the refrigerator.
To finish the dish, transfer potatoes and beef to a large platter. Pour the cooking juices into a saucepan and skim off any fat. Add in the peppers and bring to a boil over medium high heat. Whisk the cornstarch together with 1 tablespoon of cold water and pour into the sauce. Cook for 2 minutes until the sauce thickens. Pour the sauce over the beef and potatoes and serve!