Shell peas, reserving one third of tenderest pods.
Put reserved pods on a square of cheesecloth and tie corners securely together, forming a bag.
Cut out core of head lettuce.
Tear solid portion of head into pieces.
Put about half of lettuce pieces into a large saucepan; set remaining pieces aside.
Trim green tops of scallions to a length of 2 to 3 inches.
Chop and add to saucepan with reserved peas, pea pods, 3 tablespoons butter, sugar, salt, monosodium glutamate, and pepper.
Cover with remaining lettuce pieces.
Cover and cook until peas are tender, 15 to 20 minutes.
Remove from heat.
Discard pea pods.
Add the remaining ingredients to saucepan.
Toss lightly to mix thoroughly.