Combine vinegar, sugar, dry mustard, and salt in a blender; add oil in a fine stream processing constantly.
Add the chopped onions, mix and chill.
For Salad
Cook almonds with sugar in a skillet over medium heat until sugar caramelizes and the almonds are golden brown stirring constantly. Remove to waxed paper to cool.
Toss the red leaf lettuce, romaine, and spinach, mushrooms, bacon, mozzarella, parmesan, cranberries, and apples together in a large salad bowl.
Add dressing just before serving.
Garnish with some cheese and bacon.
Recipe by Cheery Kitchen at https://cheerykitchen.com/apple-bacon-salad-22/