Sear the Beef: Pat beef dry, then season with salt and pepper. Heat oil in a skillet over high heat. Sear beef in batches until browned (2–3 minutes per side). Transfer to slow cooker.
Slow Cook the Magic: Add peppers, onion, garlic, tomatoes, broth, soy sauce, brown sugar, and spices to the slow cooker. Stir gently, then cook: Low heat: 6–8 hours (best for tenderness) or High heat: 3–4 hours (if short on time).
Thicken the Sauce: Mix cornstarch + water into a slurry. Stir into the slow cooker 30 minutes before serving.
Cook the Rice: Rinse rice until water runs clear. Combine with water, butter, and salt in a pot. Bring to a boil, then simmer covered for 15 minutes. Let rest 10 minutes before fluffing.