Place oats, milk, cinnamon, and raisins in a bowl, stir to combine. Cover tightly with plastic wrap and refrigerate overnight. Just before serving, stir in apples and yogurt.
Tip: Lactose intolerant? Substitute 1/4 cup apple juice for the skim milk.
Tip: Wild about Bananas? Blend 1/2 ripe banana and 1/4 teaspoon vanilla extract until smooth. Add to muesli in place of cinnamon, raisins, and apple. Or, top muesli with your favorite fruit: peaches, plums, apricots, pears, or berries of any kind. Toasted nuts are a great addition too.