Over medium heat, saute onion until tender but not brown.
Add peas and stir to coat. Add water to just cover and simmer until tender, 3-5 minutes.
Remove from heat and let cool slightly.
Meanwhile, chop mint (chiffonade or mince).
Blend pea mixture in a food processor or with a stick blender for about 1 minute, until pureed.
Put back into pan and place on low heat, add mint and salt and pepper to taste, and additional water if desired. Squeeze in some lemon juice to taste. Keep on heat for a few minutes to blend flavors, then serve, or chill and serve cold. Garnish with additional mint and toasted almonds.