Thai-Style Stir-Fried Macaroni (Pad Macaroni)

Ingredients (14)

• 9 ounces (250 grams) macaroni (Thais use straight, smooth macaroni noodles about 1 1/4 inches long (when dry -- they are about 3 inches long when cooked), which for some reason are a bit difficult to find in some countries. You can also use bucatini /perciatelli or bigoli broken into 1- to 2-inch lengths, ziti , mostaccioli , or penne instead. Don't use elbow macaroni, of American mac 'n' cheese fame, because they are too small and curved.):
• 3 tablespoons ketchup (I know, I know! When I have it on hand, I use Stokes Bloody Mary Ketchup, which has a bit of a savory kick, but if you can't find that, you can use any spicy ketchup, or regular ketchup plus a dash of Worcestershire sauce and a dash of Tabasco sauce.)
• 1-2 tablespoons Sriracha sauce (Try to use a true Thai Sriracha sauce, rather than the Vietnamese-American Huy Fong version, which has a very different taste and is much thicker, spicier and less sweet, tangy, and garlicky than true Sriracha sauces from Sriracha, Thailand); I'd start with 1 tablespoon and add more later if you prefer the dish spicier, though it usually is not served very spicy at all.)
• 1 tablespoon soy sauce
• 2 teaspoons fish sauce
• 1 to 2 tablespoon vegetable oil (for stir-frying)
• 2 garlic cloves (peeled and finely minced)
• 1 onion (peeled and julienned into thin slices)
• 1/2 carrot (peeled and cut into thin slices)
• 9 ounces/250 grams chicken breast (cut into bite-sized pieces (you can also use pork or shrimp, if using shrimp, quickly stir-fry the shrimp separately and stir in together with the noodles at the end, before serving)
• 1 large egg
• 3 scallions (root and tips trimmed, white parts halved lengthwise and cut into 2-3 inch lengths, green parts cut into 2-3 inch lengths (keep them separate because you will add the white parts and green parts at different times)
• 2 tomatoes (cored and each cut into 8 wedges)
• Garnish: ground ​pepper (white ground, to taste, for serving)