Squeeze excess water out of thawed spinach; in a large bowl, mix spinach with onion and cottage cheese and set aside.
Season chicken breasts with Cajun-style seasoning, then place 1/4 of cheese/spinach mixture in the center of each breast and fold in half. Secure with toothpicks and place in a lightly greased 9x13 inch baking dish.
Drizzle with melted butter and bake at 350 degrees F (175 degrees C) for about 25 minutes, or until chicken is cooked through and juices run clear.
