Sprinkle beef with salt. Warm 1 Tbsp. oil in a large skillet and brown beef, in batches if necessary, on all sides, about 8 minutes total. Transfer to a slow cooker. Add remaining oil and onions to skillet and cook until softened, 3 to 5 minutes. Stir in garlic and cook 1 minute. Add to slow cooker. Stir in tomatoes, peppers, oregano, soy sauce and tapioca.
Cover and cook on low until meat is fork-tender, 7 to 8 hours. Stir in capers, season with salt if necessary and serve.