Put your food processor to work when making these tasty appetizers. Whirl the spinach, cheese, eggs, and seasoning until the eggs are beaten and the cheese is chopped.
Heat oven to 375°F. Put spinach, Havarti, Parmesan, eggs, milk, garlic powder, oregano, pepper and nutmeg in processor. Pulse until cheese is finely chopped.
Place mushroom caps on 11 x 15 x 1/2-inch baking pan. Coat mushrooms with cooking spray; sprinkle with salt. Fill each cap with 1 level tablespoon spinach mixture. (Can be made a day ahead; refrigerate, tightly covered.)
Bake in 375°F oven 25 minutes or until the mushrooms are tender and the filling is set.