Preheat oven to 350°F (177°C) degrees. Line the bottom of a 13 x 18 inch half sheet baking pan with aluminum foil or parchment running in both directions. Leave an overhang on all sides so you can lift the bars out before cutting. Spray with cooking spray and set aside.

In a very large bowl, stir the oats, flour, brown sugar, and cinnamon until combined.  Cut in the cold butter using a pastry blender or two knives. You want it in pea-sized pieces.  Remove 2 cups of the mixture to a small bowl and add the pecans. Set this mixture aside.  You'll use it later for the topping.

Press the remaining flour oat mixture evenly onto the bottom of the prepared baking sheet. Bake for 15 minutes or until light golden brown. Meanwhile prepare the filling.

Whisk the sugar and eggs together until smooth and a pale yellow. Add the flour and salt, whisking until mixed in. Mix in the peaches.  If using canned peaches, make sure they are well drained, then fold in.   After 15 minutes, remove crust from the oven and pour the filling over the hot crust.  Sprinkle with the remainder of the reserved topping mixture.

Bake for 32-35 minutes or until the top is a golden brown. Place the pan on a wire rack and let cool in the pan for about 30 minutes. Transfer bars to the refrigerator to cool further for 2 hours. Once cold, remove the bars from the pan using the overhanging parchment. Cut the bars into squares.

Stir the confectioners' sugar, cream, and vanilla extract together until smooth. Drizzle generously over each square.