Did you mean to add the spinach to step 2?

I imagine you should add in the spinach after the onion/garlic mixture is removed from the heat. Presumably your spinach would be at room temperature, and might overcook a bit if heated too much. If you waited until the mixture was cooled down a bit, and added it just before you add in the eggs and breadcrumbs, it would be much easier to handle for stuffing the chicken.