Like the too much salt remedy, try adding a peeled potato to see if it will absorb some of the strong flavor... You can also try adding sugar to counteract the strong onion flavor. Nothing to lose.
Moisture turns it into a rock. Put some rice in it. After, throw it away
1/8 teaspoon onion powder equals 1 tablespoon minced onion
also read as this:
1/8 teaspoon onion powder equals 1/16 cup of minced onion
Obviously, it depends on the amounts of all the other ingredients. In a normal-sized pot serving about 10 people, I'd put in roughly 2 tablespoons. The nice thing is that onion powder is relatively subtle, so you really can't mess up too badly. A little more or a little less won't make a significant difference in flavor.