Heat a cast-iron or other oven-safe large skillet over medium-high heat.
Add chicken, and onions and stir fry until browned.
Add garlic, cumin and coriander, salt and pepper and cook for a further minute or two.
Add cilantro, chilies, and corn; stir to combine. Cook about 3 minutes or until heated.
Remove from heat and top with cheddar.
Arrange polenta slices in an even layer over the top.
Unroll crescent roll dough; separate into 8 triangles. Place the shortest side of each triangle on the rim of the skillet over cheese with points in the center.
Bake 15 minutes (up to 20 minutes) or until dough is golden brown.
Remove from oven, and let stand 5 minutes before cutting into wedges to serve.