In 1-quart saucepan, heat applesauce to boiling over medium-high heat. Stir in oats. Let stand 20 minutes.
Heat oven to 350°F. Grease bottom and sides of 9-inch square pan with shortening. In large bowl, beat 1/2 cup butter and granulated sugar with electric mixer on medium speed until light and fluffy. Beat in vanilla and eggs until fluffy. Beat in applesauce mixture just until mixed. Stir in flour, baking soda, cinnamon, nutmeg and salt, scraping bowl once, just until blended. Pour into pan.
Bake 40 to 50 minutes or until toothpick inserted in center comes out clean.
Meanwhile, in small bowl, mix all topping ingredients until well blended. Spread topping over hot cake. Broil cake with top 6 inches from heat 1 to 2 minutes or until top is golden and bubbly. Cool 30 minutes. Serve warm.