Peel and core onions, but don't cut through completely. Place on square of heavy duty aluminum foil. Place 1 tablespoon of water and a bouillon cube in center of onion. Sprinkle each onion with garlic salt and top with a pat of butter. Bring corners of foil up and twist over onion, forming a packet. Bake one hour at 350*. When done, peel back foil, top each onion with a slice of cheese and broil til cheese is melted.