Mix all ingredients in a big bowl: shredded chicken, street corn, cream cheese, cheddar cheese, sour cream, garlic powder, chili powder, salt, and pepper until combined.
Grease a 9x13 inch baking dish and spread the mixture evenly.
Bake in the oven for about 30 minutes until bubbly and golden brown on top.
Allow the casserole to rest for a few minutes.
Garnish with diced green onions before serving.
Notes
Use pre-cooked rotisserie chicken to save time. Pre-soften cream cheese for easier mixing. Use canned street corn for convenience.