Preheat the oven to 350ºF and grease an 8- or 9-inch square baking dish.
In a large bowl, combine the oats, flax, maple syrup, water, oil, salt, pumpkin pie spice, baking powder, vanilla, and pumpkin. Stir well, then fold in the pecans and cranberries, if using. (I like to reserve a handful of pecans for sprinkling on the top.)
Pour the oatmeal mixture into the greased pan, then smooth the top with a spatula. Sprinkle the reserved pecans over the top, if desired. Bake until golden on top, about 40 minutes at 350ºF.
Let the baked oatmeal cool for 10 minutes, then slice and serve. If you'd like this to be slightly sweeter, you can serve with extra maple syrup for drizzling.
Leftover baked oatmeal can be stored in an airtight container in the fridge for up to 5 days, or you can freeze it for up to 3 months.
Nutrition information is for 1 of 6 slices, or 2 muffin cups. This information is automatically calculated, and is just an estimate not a guarantee.This recipe has been tested with old-fashioned oats, not quick cooking oats. I imagine quick oats will work, too, but the texture might be slightly more mushy.If you want to make this recipe with mashed banana instead, try my Banana Baked Oatmeal Cups.