First, preheat oven to 350ºF and line an 8x8-inch baking dish with parchment paper.
Mix all of the dry ingredients in a large mixing bowl until combined.
Then, whisk all of the wet ingredients into a separate bowl. Add the dry ingredients to the wet ingredients and mix.
Transfer the batter to a baking dish and bake at 350ºF for about 30 minutes or until the top begins to brown. If the middle of the oatmeal bake isn’t baking, cover the bake with tin foil and bake for an additional 5 minutes.
Remove from oven and let the oatmeal bake cool for 5 minutes.
While the oatmeal bake is cooling, heat all of the ingredients for the tres leches in a small saucepan over medium heat. Bring to a simmer and then remove from heat.
Slice the oatmeal bake into squares and serve in a bowl with 1-2 tablespoons of the tres leches. Top with whipped cream, fresh berries, or vanilla Greek yogurt.