Soak pad thai rice noodles in hot water for 5-10 minutes until tender but not mushy. Drain and set aside.

Heat vegetable oil in a wok or large skillet over medium-high heat.

Add egg and stir until barely set, about 30 seconds.

Add shrimp (if using) and cook, stirring, until shrimp and egg are almost cooked through, 2-3 minutes.

Add tofu and radish and cook for 30 seconds.

Add noodles and cook for 1 minute.

Stir in bean sprouts.

Add tamarind water, fish sauce, and simple syrup and stir-fry until sauce is absorbed by noodles and noodles are well coated, about 1 minute.

Stir in chopped garlic chives.

Add 1/4 teaspoon ground chiles and 1 tablespoon peanuts and toss well.

Transfer to serving plates.

Garnish with remaining 1/4 teaspoon ground chiles, 1 tablespoon peanuts, and lime wedges.