Line half sheet pan with parchment paper. Attach a 2-inch-high pan extender.
Bring water, oat milk, sugar and salt to boil in large saucepot. Stir in oats; return to boil. Cook about 10 min. or until oatmeal is thick, stirring constantly. Remove from heat and let cool 10 min. Stir in 1-1/2 lb. cookie pieces. Spread into prepared pan. Refrigerate several hours or overnight. Cut chilled oatmeal 4 x 5 into 20 pieces. Cover and refrigerate until ready to serve.
For Each Serving: Heat 1 Tbsp. oil in skillet on medium heat. Add 1 oatmeal piece. Sauté 2 to 3 min. on each side or until golden brown and internal temperature reaches 165°F. Place on serving plate. Top with 5 raspberries, 4 blackberries, 5 blueberries, 1/2 oz. of the remaining cookie pieces and 1 oz. maple syrup.