Cook onion and green pepper until almost tender in hot oil in a large skillet; stir occasionally.
Mix in the tomato soup, soy sauce, brown sugar, and lemon peel and juice.
Bring to boiling; simmer 5 minutes.
Mix in the tuna, separating it into small pieces.
Serve with fluffy hot cooked rice.
Garnish with toasted sesame seed and chow mein noodles.