Melt butter in a skillet over medium-high heat. Add onion, and sauté 5 minutes or until tender. Stir in soup and next 5 ingredients. Reserve 1 cup sauce.
Drain spinach well, pressing between layers of paper towels.
Stir together spinach, cottage cheese, and next 3 ingredients.
Place 3 lasagna noodles in a lightly greased 13- x 9-inch baking dish. Layer with half each of sauce, spinach mixture, and chicken. Sprinkle with 1 cup Cheddar cheese. Repeat procedure. Top with remaining 3 noodles and reserved 1 cup sauce. Cover and chill up to 1 day ahead.
Bake at 350° for 45 minutes. Sprinkle with remaining 1 cup Cheddar cheese, and bake 5 more minutes or until cheese is melted. Let stand 10 minutes before serving.