Preheat the oven to 350°F.
In a small bowl, combine the sorrel, lemon juice and 1/4 cup olive oil. Season with salt and freshly ground black pepper and whisk to combine. Set aside.
Place the spring onions on a large baking sheet. Drizzle with 2 tablespoons olive oil and sprinkle with sea salt. Put the onions in the oven and cook for 40 minutes or until they are soft and caramelized. Remove from the oven.
Transfer the onions to a serving platter. Spoon the sorrel mixture over the top. Serve immediately.