1. Preheat oven to 425°.
2. Heat a large ovenproof skillet over medium-high heat. Coat pan with cooking spray. Add chicken to pan; sauté 4 minutes on each side. Place skillet in oven; bake at 425° for 10 minutes or until done. Remove chicken from pan; let stand 15 minutes. Remove meat from bones; shred. Discard bones. Place chicken in a medium bowl. Add 1 1/2 tablespoons cilantro, corn, and next 5 ingredients (through black pepper) to chicken; toss to combine.
3. Return pan to medium-high heat. Add 1/2 cup onion; sauté 5 minutes, stirring occasionally. Add 3 garlic cloves; sauté 30 seconds, stirring constantly. Add onion mixture to chicken mixture; stir to combine.
4. Combine remaining 1 1/2 cups onion, remaining 3 garlic cloves, broth, salsa, 1/4 cup water, and jalapeño in a medium saucepan over medium-high heat; bring to a boil. Reduce heat, and simmer 15 minutes, stirring occasionally. Remove from heat; let stand 10 minutes. Carefully pour mixture into a blender; add 2 tablespoons cilantro. Process until smooth.
5. Heat a large skillet over medium-high heat. Add 2 tortillas; cook 1 1/2 minutes on each side. Remove tortillas from pan; repeat procedure with remaining tortillas. Cut tortillas into quarters.
6. Spread 1/2 cup salsa mixture in the bottom of an 8-inch square glass or ceramic baking dish coated with cooking spray. Arrange 12 tortilla quarters over salsa mixture. Spoon half of chicken mixture over tortillas. Repeat layers, ending with tortillas. Pour remaining salsa mixture over tortillas; sprinkle evenly with cheddar cheese. Bake at 425° for 15 minutes or until bubbly and lightly browned. Top with remaining cilantro.