Heat oven to 350°F. Spray bottom and sides of 13x9-inch pan with cooking spray. In small bowl, stir 1 cup baking mix, the brown sugar and cinnamon. Cut in butter, using pastry blender (or pulling 2 table knives through ingredients in opposite directions), until crumbly; set aside.
Add enough water to 1/4 cup reserved peach juice to measure 2/3 cup. In large bowl, beat juice mixture, 3 cups baking mix, the granulated sugar, vanilla, nutmeg and egg with electric mixer on low speed until blended. Pour batter into pan; spread evenly. Place peach slices on batter. Sprinkle streusel over top.
Bake 25 to 30 minutes or until toothpick inserted in center comes out clean. Cool 45 minutes. Serve warm or cool.