Cut the beef, onion, green onion, spicy green chili pepper, and mushrooms into bite-sized pieces.
Add cooking oil to a pan and stir-fry the beef.
When the beef is about halfway cooked, add onion, green onion, mushrooms, and spicy green chili pepper, then stir-fry.
Add low-sugar gochujang, soy sauce, minced garlic, and erythritol instead of sugar, and mix well.
Stir-fry until all ingredients are fully cooked.
Transfer to a plate and finish with sesame oil and sesame seeds.