Cook rice noodles in boiling water according to package directions until al dente, then drain and toss with a splash of neutral oil to prevent sticking. Set aside while you prepare the other components.

Heat 2 tablespoons neutral oil in a large skillet or wok over medium-high heat. Add minced garlic and sauté for 30 seconds until fragrant but not browned. Add mixed vegetables and stir-fry for 2-3 minutes until tender-crisp and bright in color.

Push vegetables to one side of the pan and add patted-dry shrimp to the empty side with Szechuan peppercorns and 2 tablespoons chili oil. Cook 3-4 minutes until shrimp turns pink and opaque throughout, stirring occasionally to prevent peppercorns from burning.

In a small bowl, whisk together soy sauce, rice vinegar, brown sugar, and remaining 1 tablespoon chili oil until sugar dissolves. Pour this sauce over the shrimp and vegetables, stirring everything together to coat evenly.

Add cooked noodles to the skillet and gently toss for 2 minutes using tongs until noodles are well coated with sauce and heated through. The noodles should glisten with the spicy sauce.