In a large pot of salted boiling water, cook noodles until al dente. Drain.
In a small bowl, whisk together lime juice, brown sugar, fish sauce, soy sauce, and cayenne pepper. Set aside.
In a large nonstick pan over medium-high heat, heat oil. Add capsicum and cook until tender, about 4 minutes. Stir in garlic and cook until fragrant, about 1 minute more. Add the meat of choice and season with salt and pepper.
Push meat and vegetables to one side of the pan and pour in the egg. Scramble until just set then mix with the meat mixture. Add the cooked noodles and toss until combined. Pour in the lime juice mixture and toss until the noodles are coated.
Garnish with green onions and roasted peanuts before serving.