Begin by bringing a large pot of water to a boil. Once boiling, add the rice noodles and cook according to package instructions, typically for about 4-6 minutes. Once cooked, drain and set aside.
While the noodles are cooking, prepare your vegetables: slice the onion, mince the garlic, slice the bell pepper, julienne the carrots, and chop the green onions.
In a wok or large frying pan, heat the vegetable oil over medium-high heat. Add the sliced onion and garlic, and stir-fry for about 1-2 minutes, until fragrant.
Add the bell pepper, broccoli, and carrots to the wok. Stir-fry for an additional 4-5 minutes, or until the vegetables are tender but still crisp.
Lower the heat to medium, and add the cooked rice noodles to the pan. Pour in the soy sauce, chili sauce, and sesame oil. Toss everything together for about 2-3 minutes until evenly combined and heated through.
Season with salt and pepper to taste, and sprinkle the chopped green onions on top.
Serve your spicy stir-fried rice noodles hot, garnished with fresh cilantro and lime wedges if desired.