Grease a 9x9 or 8x8 silicon pan and place it onto another metal pan to keep it flat. Pre-heat oven to 400 degrees Fahrenheit.
In a large bowl mix together oatmeal, melted butter, corn syrup, sugar, salt, and vanilla. Pour contents into silicon pan.
Bake uncovered in oven for about 8 minutes or until the surface is bubbling and has turned a slightly darker brown.
Remove from oven and sprinkle the semi-sweet chocolate chips over the surface while still hot and bubbling. Let the chips soften, even placing back into oven for a few minutes if needed.
When the chips are soft, take a fork and spread the chocolate evenly over the surface.
Sprinkle chopped nuts over the melted chocolate if desired.
Once done, place the silicon pan (still on the metal pan to keep it flat) in the refrigerator to cool for minimum of 2 hours.
After the bars have cooled, remove from the refrigerator and turn the silicon pan upside down over a cutting board. It should be one solid piece, be careful peeling back the silicon as it may still try to stick to it.
Using a long chopping knife, cut out the size and shape of the bars. Refrigerate until ready to eat!