Pour egg mixture over onion and mushrooms and reduce heat to medium-low. As mixture begins to set, gently move spatula across bottom and sides of skillet to form large, soft curds. Cook until eggs are just partially set. Remove from heat.
Spray 2-quart (2 L) baking dish with cooking spray. Spoon half of scrambled eggs into baking dish. Sprinkle half of broccoli and cheese over top. Repeat layers.
Bake in preheated 325°F (160°C) oven until hot, about 15 minutes.
Notes
A heaping 1/4 tsp (1 mL) each dried basil, thyme and oregano can be used instead of vegetable seasoning.