This dish is 5 stars! Comfort heaven!

2 pounds boneless, skinless chicken breasts
1 packet ranch seasoning mix
1 can (10.5 oz) cream of chicken soup
1 cup sour cream
2 cups shredded cheddar cheese
1 small onion, finely chopped
1 bag (32 oz) frozen Tater Tots
Salt and pepper to taste
Chopped fresh parsley for garnish (optional)