Put the flank steak in the freezer for a few minutes to aid in thinly slicing safely.
Heat 1/2 cup oil in a small skillet over medium heat. Dredge the shallot slices in the cornstarch and shake off any excess. Add the shallots into the heated oil and remove them to a paper-towel lined plate when they become a light golden-brown color.
Bring a large pot of water to a boil over medium heat. Salt the water and add the pasta. Cook to al dente.
While pasta water comes to a boil, stem and thinly slice the mushrooms, and seed and thinly slice the sweet and hot peppers.
Remove the meat from the freezer and thinly slice into 1/4-inch wide by 2-inch pieces.
Heat the remaining 2 tablespoons of oil in large skillet or wok over medium-high heat. Add the beef and cook in a single layer for 2 to 3 minutes. Turn the meat over and add shiitakes, sweet and hot peppers, garlic and scallions. Stir-fry 2 to 3 minutes, then add the curry paste, fish sauce and stock and bring to a boil. Add in the edamame, and cook for 1 minute to heat through, then add the basil.
Drain the pasta and put into a large serving bowl. Add the beef mixture, the lime zest and lime juice. Toss vigorously and season with some black pepper, to taste. Garnish with the fried shallots sprinkled on top.