Preheat the oven to 375 °F. Lightly spritz a 9x13-inch baking dish with nonstick spray.
In a large bowl, whisk together the nonfat Greek yogurt and sugar.
Whisk in the egg and egg white, making sure the egg is well-beaten and fully incorporated.
Whisk in the baking powder, salt, and vanilla extract.
Zest an orange - you're looking for maybe about 2 teaspoons of orange zest. After that, cut the orange in half and juice it (or use bottled OJ, it's fine) Add the orange zest and about ½ cup of orange juice to the bowl and whisk it in with the rest of the ingredients.
Stir in the milk
Stir in the oats
Stir in the cranberries -- don't thaw if frozen.
Pour the oatmeal mixture into the prepared baking dish and bake in the oven for about 45 minutes, until the edges are lightly brown and a knife or toothpick inserted into the center of the oatmeal comes out clean. If you're using frozen cranberries, you may need to cook this a little longer. It might take about 1 hour if the berries were frozen, so keep an eye on the oven!