Preheat oven to 400°F.
In a large sauté pan, add a drizzle or so EVOO and sweat out garlic. Add spinach, stir to warm through. Season with salt and pepper; add lemon juice and nutmeg.
Combine the leftover rice, vegetables, chicken, lemon zest and feta with the cooked spinach mixture. Place everything in a casserole dish.
In a saucepan, melt the butter over medium heat. Whisk in the flour and cook, stirring, for 2 minutes. Whisk in the milk and cook until thickened slightly; season with salt, pepper and nutmeg. Remove the sauce from the heat, temper egg yolk then add it to the béchamel.
Top your casserole dish with béchamel and sprinkle the top with Parm. Place in oven to bake for about 30-40 minutes or until browned and bubbly.