Place sausages in cold skillet.
Cover and cook over low heat about 10 minutes until most of the fat has cooked out.
Meanwhile, combine baked beans and mustard, onion and brown sugar in shallow casserole (1-1/2 qts.)
Cut pineapple slices in half; arrange in border on beans.
Top with sausages, spoke-fashion.
Bake in moderate oven (375 degrees) about 20 minutes.