Cook noodles according to package directions; drain.
While water comes to a boil, combine sugar and next 4 ingredients (through Sriracha) in a small bowl.
Heat a large skillet or wok over medium-high heat. Add oil to pan; swirl to coat. Add onion pieces, shrimp, and garlic; stir-fry 2 minutes or until shrimp is almost done. Add cooked noodles; toss to combine. Stir in sauce; cook 1 minute, stirring constantly to combine. Arrange about 1 cup noodle mixture on each of 4 plates; top each serving with 1/4 cup bean sprouts, 1 tablespoon peanuts, and 2 teaspoons basil.