Cut the squash in half through the stem end and scrape out seeds and goop. Put cut-side down on a microwave-safe plate. Cover with a sheet of waxed paper and microwave on high until the orange flesh is fork-tender, about 8 minutes.
Roughly chop the pecans and mix remaining ingredients in a microwave-safe bowl.
When squash is done, take it out and cover it and the waxed paper with a clean towel to keep it warm. Microwave the filling on high until hot (about 4 minutes).
Spoon filling into squash and top with a pecan half and serve hot.