In a small skillet over medium heat, toast the sesame seeds until fragrant and light brown, about 2 minutes. Set them aside to cool.
In a large pot, boil the noodles until tender but firm to the bite, 8 to 9 minutes. Drain and rinse under running cold water and drain again. Toss with 1 tablespoon of the oil.
In a large bowl, combine the remaining vegetable oil with the sesame oil, vinegar, lime juice, honey, salt, pepper, and red pepper flakes, if using. Whisk to mix well. Add the noodles, green onions, carrots, mango, and cilantro and toss. Add more salt and pepper to taste, if needed. Refrigerate the salad for 2 hours, stirring every half hour, so that the noodles absorb the dressing evenly. Serve the salad cold with the sesame seeds sprinkled over the top.