Preheat oven to 325F. Line 2~3 baking sheets with parchment paper.
Beat together butter and sugars until smooth.
Add the egg replacer mixture (or the egg and the egg yolk) and vanilla, beat well until combined.
In a small mixing bowl, whisk together flour, oats, baking powder, baking soda and salt.
Add the flour mixture to the butter and mix until thoroughly incorporated. Scrape the sides and the bottom of the bowl.
Stir in the chocolate chips.
Using a tablespoon or teaspoon size cookie scoop, scoop the dough onto the prepared baking sheets, leaving about 11/2"~2" between the cookies.
Bake the cookies for 15 minutes (for the table size cookies) and for 12~13 minutes (for the teaspoon size cookies), until they are light brown with lightly darker edges.
Remove the baking sheets from the oven and let the cookies rest for a few minutes. Transfer them to a cooling rack once they are set enough to handle.