Preheat oven to 350° Fahrenheit and lightly grease the inside of a 9x9-inch baking dish.
Whisk together the milk, Greek yogurt, eggs, maple syrup, and vanilla extract in a large bowl.
Add in the rolled oats, cinnamon, nutmeg, carrots, walnuts, and raisins to the bowl and stir until everything is completely combined.
Pour the oat mixture into your prepared baking dish and bake for 40-45 minutes, or until the top is set and the oats are cooked through.
Remove the baked oats from the oven and let them cool completely. While the oats cool, make the frosting by adding the Greek yogurt, cream cheese, maple syrup, and vanilla extract to a bowl and use either a hand or stand mixer to whisk it together until light and fluffy.
Once the oats are completely cool, top with the frosting, cut into squares, and enjoy! Or, store the frosting separately, cut the oats into squares and store for an easy meal prep breakfast. Right before eating, top one serving of baked oats with a big dollop of frosting.