Add the broccoli, bell peppers, and carrots to the skillet. Stir-fry for 3-4 minutes until the vegetables are tender-crisp.
Push the vegetables to one side of the skillet and add the cubed tofu to the other side. Cook for 2-3 minutes until the tofu is lightly browned.
Add the cooked noodles to the skillet along with the soy sauce, dark soy sauce, sugar, sesame oil, and black pepper. Toss everything together and stir-fry for another 2-3 minutes until well combined and heated through.
Remove from heat and stir in the chopped green onions. Serve hot.
Notes
For added protein, consider using tempeh instead of tofu.
Feel free to add other vegetables like snap peas or mushrooms for more variety.