How to Make It
In a large saucepan, bring the water to a boil. Add the zucchini, onion and 1 teaspoon of salt and cook over moderate heat until the zucchini are tender, about 15 minutes. Drain the vegetables, reserving the cooking liquid. Let cool.
In a blender, combine the cooked vegetables with the spinach, heavy cream, lemon juice and mint; pulse until finely chopped. With the machine on, gradually add about 2 cups of the reserved cooking liquid and blend until smooth. Season with salt and pepper and refrigerate until chilled.
Meanwhile, gently open the zucchini blossoms and remove the yellow stamen. Cut off any spiky leaves at the base of the blossoms.
In a small bowl, beat the goat cheese with salt and pepper. Using a small spoon, fill the blossoms with the goat cheese. Gently twist the tips of the blossoms around the filling. Set them on a baking sheet and refrigerate until firm.
Preheat the oven to 350°. Bake the zucchini blossoms just until warmed through, about 6 minutes.
In a small bowl, whisk the tomato juice with the oil. Season with salt and pepper. Ladle the zucchini soup into 8 shallow soup plates. Set a stuffed blossom in the center of each. Garnish with the diced tomatoes and a drizzle of the tomato juice mixture and serve.