Bring a large pot of salted water to a boil. Add the green beans, bring the water back up to a boil, and cook for 2 minutes. Drain the beans in a colander, rinse with cold water, and drain again. Set aside. (At this point, the blanched green beans can be refrigerated in an airtight container for up to 2 days before proceeding with the recipe, if desired.)
In a medium skillet, heat the olive oil over medium heat. Add the onion and sauté until tender, about 5 minutes. Add the garlic and stir for 1 minute. Add the green beans, tarragon, and parsley. Cook to heat through, stirring often, for about 3 minutes.
Remove the pan from the heat and stir in the lemon juice, zest, and toasted almonds. Season with salt and pepper before serving.