Mix oats, milk, and sweetener(s) in a large bowl. Combine well.
If soaking to remove phytates, add acid medium (apple cider vinegar or lemon juice).
Soak either overnight (for a more baked oatmeal-type dish) or for at least 24 hours (for an Oatmeal Cake) at room temperature. Make sure to read the instructions about How to Soak Grains.
Add remaining ingredients, saving baking powder and egg substitute (if using) until last.
If using nuts and/or dried or fresh fruit, put half of the nuts and fruit in the bottom of a greased 8x8 square baking dish.
Pour the batter onto the nuts and fruit (or directly into the prepared dish if not using the nuts and fruit).
Top with the remaining nuts and/or fruit if desired.
Top with cinnamon sugar if desired.
Bake in a preheated 375 degree oven for 35-45 minutes, or until the middle of the cake is set.
Serve either warm, with additional cinnamon sugar, nuts, fruit and milk, whipped cream or yogurt. Alternatively, eat at room temperature like a regular cake.
Store in the refrigerator in a closed container or freeze for a longer shelf life.