Start by whisking together the dry ingredients (flour, baking soda, and salt) in a medium bowl. Next, cream the softened butter and brown sugar until the mixture looks fluffy. Beat in the eggs and vanilla extract. Once combined, gradually stir in the dry ingredients, then fold in the oats using a spatula.
Press about two-thirds of the oatmeal mixture into a greased 13×9-inch pan. The remaining dough will be used for the topping.
Melt the chocolate chips, condensed milk, and butter together in a heavy-bottom saucepan over medium heat. Stir continuously to prevent the chocolate from scorching. Once smooth and glossy, mix in the vanilla and chopped pecans. Remove from heat.
Spread the chocolate fudge layer evenly over the oatmeal cookie base. Take the reserved oatmeal dough and crumble it into small chunks, scattering them across the fudge layer. The scattered chunks will form the cookie topping.
Preheat your oven to 350°F. Bake the bars for 25-30 minutes, or until the cookie bits on top are golden brown. Cool the pan completely before cutting the bars into squares.