Preheat oven to 400 degrees F. Spray 8x8-inch baking dish with cooking spray; set aside. Combine ravioli, drained tomatoes, onion and taco seasoning mix in large bowl; place mixture in baking dish.
Cover with foil; bake 35 to 40 minutes or until mixture is hot and bubbly. Remove foil; sprinkle with cheese. Bake uncovered 5 minutes or until cheese melts. Place corn chips around edge of dish and lettuce in center just before serving.
One 40-ounce can of mini beef raviolis may be used in place of two 15-ounce cans. Increase taco seasoning mix to 2 tablespoons when using the large can. Continue with recipe as directed.