Preheat the oven to 375 F. Lightly coat a 9-inch pie pan with cooking spray.
Arrange peach slices in the prepared pie plate. Sprinkle with lemon juice, cinnamon and nutmeg. Set aside.
In a small bowl, whisk together flour and brown sugar. With your fingers, crumble the margarine into the flour-sugar mixture. Add the uncooked oats and stir to mix evenly. Sprinkle the flour mixture on top of the peaches.
Bake until peaches are soft and the topping is browned, about 30 minutes. Cut into 8 slices and serve warm.