HEAT oven to 350°F.
BEAT first 4 ingredients in large bowl with mixer on low speed just until cake mix is moistened, stopping frequently to scrape side of bowl. Add 1/4 cup butter; beat on medium speed 2 min. (Batter will be thick.)
SPREAD batter onto bottom of 13x9-inch pan sprayed with cooking spray. Arrange pear slices over batter, pressing lightly into batter to secure. Sprinkle with dry gelatin mix and cinnamon. Drizzle with remaining butter; sprinkle with nuts.
BAKE 40 to 45 min. or until toothpick inserted in center comes out clean.