Preheat oven to 425°F. Place tater tots in the bottom of a casserole dish and put in cold oven while it preheats. Cook until halfway done, about 15-20 minutes, then remove and set aside.
In a medium skillet, cook pork sausage over medium heat until browned. Remove sausage and set aside. Drain most grease, leaving a small amount in pan.
Add diced onions and minced garlic to skillet. Cook until soft, about 4 minutes.
Return sausage to skillet with onions and garlic. Add Rotel tomatoes, garlic powder, onion powder, black pepper, and red pepper flakes. Stir well and cook until most liquid evaporates.
Add sour cream, cream of mushroom soup, drained corn, half of the cheese, and milk. Stir well and cook until cheese melts completely.
Transfer cheesy meat mixture to the bottom of the casserole dish. Sprinkle with olives and half of the remaining cheese.
Layer tater tots on top, pressing down slightly to anchor them in the mixture. Top with remaining cheese and chives.
Bake for 20-25 minutes until cheese is melted and casserole is bubbling around edges and center.