Fill a microwave-safe plate full of corn chips in a single layer. Sprinkle the grated cheese on top. Microwave for 30 seconds on high then additional 10 seconds at a time until fully melted.
Sprinkle the tomatoes, cilantro, and onions on top then serve hot with sour cream and salsa.
Turn the broiler on high and move the rack about 5 inches from the broiler.
Fill an oven-safe plate full of corn chips in a single layer. Sprinkle the grated cheese on top. Place plate on top rack and broil until cheese has all melted. Remove from the broiler.
Sprinkle the tomatoes and onions on top. Serve with sour cream and salsa to dip.