Heat a pan with oil with oil, stir fry the bell pepper. Remove from the pan and set aside
Add the beef into the same pan with hot oil. Stir fry until halfway cooked, then add the onion, stir to combine.
Add the bell pepper, stir to mix, add the soy sauce, lemon juice and lemon zest, stir and simmer for 30 seconds. Remove from the heat and serve with steamed rice.