Preheat oven to 350 degrees.
In a large mixing bowl, mix all the ingredients except nuts/dried fruit, if using. Mix it well.
Pour the mixture into a 9x13 (or something close to that size) casserole dish. If using nuts/dried fruit, sprinkle on top.
Bake at 350 degrees for 45-50 minutes.
Remove from oven, cut and serve or cool and freeze in individual portions.
I like a chewier texture, so I like mostly steel cut oats in this. Play with the ratio to suit your own texture preferences. My version is sort of like eating a warm granola bar instead of a bowl of oatmeal.
I've tried this with frozen mixed berries and cherries, just blueberries, and a frozen smoothie mix that had berries and kale. There wasn't much kale in it, but it was good and I will be trying it with more kale next time since it's an easy way to get more greens. Every version I've tried has been good.
I'm going to try apple and sweet potato next.
I drizzled warm raspberry jam on the pictured serving. Delicious! Also great with no sweetening. Maple syrup was tasty too. I'm thinking that a maple cashew cream sauce would be beautiful drizzled across the top for a fancy brunch.