Preheat oven to 350°F. Cook and stir onion and margarine in large skillet until onion is tender. Stir in chicken, 1/4 cup picante sauce, cream cheese, and cumin. Cook until thoroughly heated. Stir in 1 cup of shredded cheddar cheese.
Spoon about 1/3 cup of the mixture into the center of each tortilla, rolling up each one and placing seam side down in a 9x13 baking dish. Top with remaining picante sauce and shredded cheddar cheese.