Wash squash well; leave whole and cook, covered, in a small amount of boiling salted water for about 15 minutes, or until just tender.
Combine melted butter or margarine, peas and sugar; place lettuce leaves over all.
Cover tightly and cook over low heat for 8 to 12 minutes, or until peas are just tender.
Add pimiento; season with salt and pepper.
Scoop out the seeds and a little of the pulp from the center of each squash to form cups; fill each with about 3 tablespoons of cooked peas.