This one's easy. The proportions below should make enough for four people.
4 cups of strained chicken stock or beef stock
2/3 cup of shredded raw spinach (watercress or chervil) or 1/4 cup of chopped spinach, cooked
1/2 cup of cooked peas
1/4 cup of diced raw carrots
salt to taste
Just put all the ingredients into a saucepan and let them simmer for about 5 minutes, salting to taste when the mixture is hot.
For more soup recipes, see Make Superlative Homemade Soups All Year Long