1. Preheat oven to 400°. Melt butter in a large skillet over medium-high heat. Add frozen vegetables, and sauté 4 to 5 minutes or until tender. Transfer to a medium bowl; stir in soup, diced tomatoes, and chili powder.
2. Layer half of chicken in a lightly greased 13- x 9-inch baking dish. Top with half of soup mixture and 1 cup Cheddar cheese. Sprinkle with 1 1/2 cups tortilla chips. Repeat layers once. Top with remaining 1 cup cheese.
3. Bake at 400° for 25 to 30 minutes or until bubbly. Let stand 10 minutes before serving. Garnish, if desired.
*1 teaspoon chili powder and 1/8 teaspoon ground red pepper may be substituted.