Score bread within 1/2 inch from bottom in 1 inch sections.
Turn and do the same in the other direction.
Stuff sections with cheese & mushrooms.
Sprinkle onions, poppy seed and Lawry's over top.
Melt butter. Add lemon juice and dry mustard.
Spoon over bread.
Wrap in foil.
Bake at 350 for 40 minutes.