Warm oil in a large skillet over medium-high heat. Add beef and cook, turning, until browned on all sides, 5 to 7 minutes. Remove to a slow cooker and pour off all but 2 Tbsp. fat from skillet.
Add onions to skillet and cook, stirring, until softened, 3 to 5 minutes. Add garlic and sauté 1 minute longer. Stir in paprika, caraway seeds, tomato paste and chicken broth. Bring to a boil, stirring to pick up any browned bits on bottom of skillet, and pour over beef in slow cooker. Add bell pepper, cover and cook on low for 6 hours.
Season with salt and pepper. Serve hot, with sour cream on the side, if desired.