In a large pot of boiling salted water, blanch the fiddleheads until they are crisp-tender, about 3 to 5 minutes. Remove the fiddleheads from the water and shock them in a bowl of ice water (unless you are going to use them immediately).
Drop angel hair pasta into the same pot of boiling water used for fiddleheads. Boil for 3 to 5 minutes or until al dente.
Meanwhile, in a large skillet, heat olive oil. Saute fiddlehead ferns, green onions, and red pepper flakes for 2 minutes. Drain pasta and add to skillet. Toss with truffle oil and salt and pepper. Divide pasta among 4 plates and garnish with grated cheese.