Bring a large pot of salted water to a boil and cook macaroni until just al dente; drain and set aside.
Melt butter in a saucepan over medium heat and whisk in flour, cooking for 1 minute to form a smooth roux.
Add Thai red curry paste to the roux and cook, stirring, for 30 seconds until aromatic.
Gradually whisk in coconut milk and whole milk, stirring to avoid lumps, and bring to a gentle simmer.
Stir in cheddar and mozzarella cheeses until fully melted and creamy.
Season the sauce with soy sauce, lime juice, brown sugar, salt, and black pepper.
Add bell pepper, broccoli, and snap peas; cook for 3–4 minutes until vegetables are tender yet vibrant.
Fold cooked macaroni and sliced scallions into the sauce, coating evenly.
Serve hot, garnished with chopped cilantro and lime wedges.