Soak the rice noodles in warm water for about 10 minutes. They should be bendy but not soggy. Drain and set aside.
Mix all the sauce ingredients in a small bowl. Taste it. Add more sugar or fish sauce if needed—get it to a spot you love.
Heat oil in a big pan. First cook the chicken until nearly done (3–4 minutes). Add shrimp and stir-fry until pink and just cooked through. Transfer both to a plate.
Sauté the onion until soft in the same pan. Add garlic and stir until it smells amazing. Push everything to one side, crack in the eggs, and scramble gently. Stir them in.
Add noodles and pour in your sauce. Toss it all so the noodles soak it up. Return the cooked shrimp and chicken. Add bean sprouts and scallions. Stir-fry everything for another minute. You want things hot and coated.
Scoop into bowls. Top with crushed peanuts, a lime wedge, and chili slices if you’re feeling spicy.