Add the ground beef, bell pepper, onion, garlic, ginger and chili flakes in a skillet and cook until beef is no longer pink. Drain any excess fat and return skillet to stove top.
Meanwhile whisk together the soy sauce, dry sherry, sesame oil and sugar in a small dish and pour into ground beef mixture over medium high heat. Combine the cornstarch and water in the small dish and whisk until smooth. Pour into the ground beef mixture and cook until sauce thickens.
Stir in the peanuts and garnish with diced green onions if desired. Serve over hot white rice and enjoy!