Bring large pot of water to a boil. Add spinach and scallions, stirring and submerging until wilted, about 2 minutes. Drain well. When cool enough to handle, squeeze out excess water. Finely chop.
Melt butter in medium-size saucepan over medium heat. Sprinkle with 3 tablespoons flour; whisk until blended and cooked slightly, about 1 minute. Add milk, whisking to prevent lumps. Bring to a low boil over medium heat, about 3 minutes, whisking in 1 teaspoon salt, the nutmeg and cayenne. Remove saucepan from heat. Whisk in cheese; let cool slightly.
Heat oven to 375 degrees F. Lightly coat eight (7-ounce) oval baking dishes or 10-cup oval or souffle dish with nonstick cooking spray. Sprinkle with bread crumbs, tilting dish to coat.
Whisk half the cheese mixture into egg yolks in large bowl. With wooden spoon, vigorously stir in remaining cheese mixture and the spinach and scallions.
With clean beaters, beat together egg whites, remaining 1/4 teaspoon salt and the lemon juice in large clean bowl until stiff peaks form. Sift remaining 3 tablespoons flour over egg whites and gently fold in. Stir a quarter of beaten egg whites into spinach mixture to lighten. Gently fold in remaining whites. Spoon about 1 cup into each individual dish or scrape whole amount into souffle dish. Place individual dishes on baking sheet.
Bake individual souffles in 375 degree F oven until golden brown and puffed, 20 to 25 minutes, or 35 to 40 minutes for souffle dish. Serve immediately. Makes 8 individual souffles or 1 large souffle.