This is what slow cookers were invented for - Cooking stuff low and slow and long. And this is the very basic in beef stews for the slow cooker. Really delicious as it is written, from here you can develop a world class stew. Add an assortment of spices, your favorite red wine, different vegetables. This will give you the foundation to do even more wondrous things - Not to mention it is knock-your-socks-off good just as is!
In a heavy skillet over medium-high heat, heat 1 Tablespoon of the oil. In batches, sear the beef pieces well, turning to sear most of the sides of each chunk. Season each batch with a pinch of kosher salt and a few grinds of black pepper as they sear. Remove the browned pieces to your slow cooker and repeat the process with more oil and more beef pieces until all the beef is browned. Note 1: Arm roast and chuck roast are nicely marbled and very flavorful - I highly recommend either in this stew. Note 2: Don't put more than about a quarter of the meat in the pan at one time. Crowding the meat pieces together will cause the meat to "steam" and release much of its moisture. That will dry the meat and reduce its ability to really brown nicely and it will not leave nice burned flavor-chunks ("fond") on the bottom of the pan. Note 3: You don't need to cook the beef pieces through, but just brown the outside. They will finish cooking in the crock pot.
In the same pan, and using a little more oil if needed, cook the onions until they are beginning to soften, about 4 minutes. Season them with a little salt and pepper. Add the garlic and stir until it is fragrant, about 30 seconds. Move the cooked onion/garlic mixture to the slow cooker.
Once the meat and onion/garlic mixture are in the slow cooker, sprinkle on the flour and chili powder. Stir it all around to coat everything.
Add the potatoes, carrots, the tomatoes with their juice and the water. Put the lid on and cook on "low" setting for about 7 hours. If you are going to use the corn and/or peas, put them in and cook for an additional 1 hour. Note: If the sauce has not thickened, turn the heat up to high and bring the pot to a boil. Stir. The sauce does need to boil in order for the flour you added make the sauce thicken. If it still is not thick enough for your taste, stir 1 tablespoon of cornstarch with a couple tablespoons of cold water, then slowly stir it into your boiling pot.