In a medium bowl, stir together 1 cup rolled oats, 1/3 cup chopped pecans, 1/3 cup dried cherries, 1/3 cup unsweetened flaked coconut, 3 tablespoons ground flaxseed, 1/2 teaspoon cinnamon, and a pinch of kosher salt.
Grate the apple and stir the grated apple into the oat mixture until evenly distributed.
In a smaller bowl or measuring cup, whisk together 1/2 cup milk, 1/2 cup yogurt (plain Greek works well), 1 teaspoon lemon or orange juice, and 1 teaspoon vanilla extract until smooth.
Pour the milk-yogurt mixture into the oat-apple mixture and stir until everything is evenly moistened and combined.
Cover the bowl or transfer the mixture to an airtight container and refrigerate overnight (at least 6 hours).
In the morning, stir the muesli, add a little extra milk if you prefer a looser texture, and top with your choice of fruit, nut butter, nuts, seeds, a sprinkle of cinnamon, or other crunchy toppings. Enjoy!