Separate bacon pieces and place over bottom of a 3 quart casserole; cover with a lid or wax paper.
Microwave on HIGH (100%) for 5 minutes, stirring after 3 minutes.
Stir in onions.
Microwave, uncovered, on HIGH (100%) for 3 minutes or until onions are soft.
Stir in pork and beans, mustard, pineapple, chili sauce, and salt.
Cover dish with a lid or plastic wrap.
Microwave on MEDIUM (50%) for 45 minutes, stirring every 15 minutes.
Uncover and microwave on HIGH (100%) for 10 minutes, stirring every 4 minutes.
If made ahead, cool, cover, and refrigerate until next day.
To reheat, microwave, uncovered, on MEDIUM (50%) for 12 to 15 minutes (stirring every 5 minutes) or until heated through.