In a small bowl, whisk the minced shallot, orange juice, sherry vinegar, soy sauce, and sea salt to combine. Slowly drizzle in the olive oil, whisking until emulsified.
Prepare an ice bath in a large bowl and set a big pot of cold water over high heat. Add a generous amount of sea salt. Blanch green beans for 1 to 2 minutes, until bright green; immerse in ice water, drain, and blot dry.
Place a large skillet over medium-high heat. Add 1 teaspoon of the grapeseed oil. Toss half of the green beans in the skillet along with a pinch of sea salt. To get a nice sear, you'll want to give the green beans (and later, the fiddleheads) plenty of room in the skillet. It's best to cook them in batches. As you fry each batch, keep a close eye on the heat—it should be as hot as possible without causing the oil to smoke. Adjust as needed.
Fry, undisturbed, for 2 to 3 minutes, or until beans are nicely browned, flip, and cook for 2 to 3 minutes more. Repeat for second batch of green beans.
Meanwhile, boil fiddleheads in the same salted water for 8 to 10 minutes. Remove from water with a slotted spoon and blot dry with paper towels. In the same pan used to fry the green beans, add 1 teaspoon grapeseed oil over medium-high heat and then toss in the fiddleheads. Sprinkle with sea salt. Fry each side, undisturbed, for 2 to 3 minutes, or until edges have browned.
Toss radicchio and escarole with several tablespoons of the sherry vinaigrette. Top with the warm green beans and fiddleheads and a generous drizzle of vinaigrette.