Heat skillet over medium/high heat. Put 1/2 tablespoon oil in pan with the chopped onion. Cook until translucent and remove from pan. Reduce heat to medium and melt 2 tablespoons butter. Wisk in flour and cook for about 45 seconds until golden brown. Wisk in two cups milk and stir until thickened. Add nutmeg and pepper, thawed/drained spinach and cooked onion. Stir until combined. Transfer to a oven safe dish. Mix parmesan and bread cumbs in a bowl and then cover the spinach mixture with it. Broil in the overn until top is golden brown.