1. Heat a large nonstick skillet over medium-high heat. Add oil to pan; swirl to coat. Add onion, poblano chile, and garlic to pan; cook 6 minutes or until vegetables are tender, stirring frequently.
2. Stir in chile powder, tomatoes, and tomato sauce. Place half of tomato mixture in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until almost smooth. Pour into a large bowl. Repeat procedure with remaining tomato mixture.
3. Coat a 5-quart round electric slow cooker with cooking spray; place 3 tablespoons tomato mixture in bottom of slow cooker. Combine remaining tomato mixture, chicken, corn, and beans.
4. Place one tortilla on sauce in slow cooker; pour 1 cup chicken mixture over tortilla; sprinkle with 1/3 cup cheese. Top with another tortilla. Repeat procedure with remaining chicken mixture, tortillas, and cheese. Cover and cook on LOW for 2 hours or until cheese melts and edges are lightly browned. Garnish with cilantro, if desired. Cut into 8 wedges.