While spinach is not high in iron, it is higher than most other green veg I believe. Here is my tasty, super easy, spinach and pea soup:
1 onion, finely chopped
Back of spinach/baby spinach (frozen is fine too but just adjust amounts)
1-2 cups frozen peas
Chicken/vegetable stock
Lemon juice
Nutmeg
Greek yoghurt to serve
Gently fry onion in a little olive oil until soft and translucent.
If using fresh spinach, add with a little of the stock and allow to wilt before adding the peas and enough stock to just cover peas and spinach.
If using frozen, you can just add the spinach and peas then top up with sufficient stock to just cover cover the veg (if you try to top up the fresh spinach you have too much liquid).
Cook for approximately 10 minutes.
Allow to cool slightly then use a stick blender to whiz it all up. Add a dash of nutmeg, a squeeze of lemon juice and salt and pepper to taste.
At this point, it will be a very dark green, and quite thick. It's not HUGELY appealing. But store it like this in fridge or freezer.
To serve, pour hot soup into individual bowls and stir in a generous tablespoon (or more if you prefer) of greek yoghurt to each bowl. The colour fades to a gorgeous light vibrant green and the yoghurt adds a lovely tang to the flavour.
I often keep a bowl of this in the fridge and use it for lunches for a few days in a row. The peas add a slight sweetness which goes really well but to up the iron use a higher ratio of spinach to peas.