Boil water: Bring a pot of water to a boil in order to prepare your noodles according to package directions.
Sizzle the aromatics: Take the smallest pan you own and stir together peanut oil, the white parts of the scallions, minced garlic, minced ginger, and chili flakes. Heat over medium. Let the aromatics sizzle for 2-3 minutes, stirring occasionally. This will remove the raw bite of the garlic and onion, and extract flavor from the chili flakes. Remove from heat and allow to cool slightly.
Make the garlic peanut sauce: To a mixing bowl, add peanut butter, soy sauce, rice vinegar, (optional) maple syrup, the sizzled aromatic mixture, fresh lime juice, toasted sesame oil, and about 3 tablespoons water. Whisk together to form a sauce. Whisk in extra water 1 tablespoon at a time to achieve a smooth and pourable texture. Taste and adjust to preference.
Cook the noodles: Cook the noodles according to package directions, then drain them. Reserve a few tablespoons of the cooking water in case you need to thin out the sauce. You can serve this noodles hot or cold. For cold noodles, rinse the noodles thoroughly with cool water.
Toss together: Add the cooked noodles to the mixing bowl with the garlic peanut sauce and toss to coat. Add reserved cooking liquid as needed to achieve a velvety texture.
Serve: Plate the noodles and top with fresh carrots, cucumber, and red bell pepper. (Or you can toss these with the noodles and sauce in the bowl.) Top with the green parts of the scallions, crushed peanuts, and any additional toppings you like. I always like to serve with Simple Pan-Fried Tofu to boost the protein.