Partially cook onions in small amount of boiling salted water till nearly tender, about 25 minutes; drain.
Cut the patty pan squash into quarters.
Cut the red peppers into large squares.
In small saucepan combine butter, salt, and pepper; heat till butter melts.
On four skewers alternately thread wedges of squash, the onions, and pepper squares.
Grill over medium coals till done, 20 to 25 minutes.
Turn frequently and brush with the seasoned melted butter.