Place frozen spinach in the microwave in a covered bowl with a few teaspoons of water. Microwave around 4-5 minutes. Remove carefully and drain off the water, pressing the water out of the spinach with a slotted spoon or spatula. Add 1 teaspoon of onion powder, 1/2 teaspoon garlic salt, 1 cup of cheese, and mayonnaise. If you like, you can add around 1/4 to 1/2 teaspoon cayenne pepper. Mix well and spread across the top of the potatoes. Be sure the unit is on High.