Preheat oven to 350 degrees F. Spray a jelly roll pan (15 x 10) with cooking spray. (Can use 13 x 9 pan if a thicker cake is desired.)
Mix together flour, baking powder, and salt. Add softened margarine, cup of vegan sugar, soy milk, and vanilla. Mix with an electric mixer at low speed. Spread mixture into jelly roll pan.
Mix together the 3/4 cup vegan sugar and the cinnamon. Sprinkle one-half of this mixture over the cake batter in pan. Over this, layer the peach slices in even rows, lengthwise. Then sprinkle with remaining vegan sugar/cinnamon mixture. Drizzle the 2 Tbsp. melted margarine over this.
Bake for 30 - 35 minutes, until the cake peeking through the peaches has turned a golden brown.