Toss tofu cubes with cornstarch until coated. Heat 3 tbsp oil in a large skillet over medium-high heat. Fry tofu until golden on all sides, about 8 minutes. Remove and set aside.
Cook rice noodles according to package directions. Drain and set aside.
In the same skillet, heat 1 tbsp oil over medium heat. Add curry paste and cook, stirring, for 1 minute until fragrant.
Pour in coconut milk and stock. Add soy sauce and brown sugar. Bring to a simmer.
Add bok choy and cook until just wilted, 2 minutes.
Add cooked noodles and tofu to the broth. Toss to combine and heat through.
Divide among bowls. Top with cilantro and spring onions. Serve with lime wedges.