In a small bowl, whisk together the soy sauce, dark brown sugar, lime juice, water, Sriracha sauce, and minced garlic. Set it aside; this will be the flavor base for your noodles.
Heat 2 tablespoons of vegetable oil in a large skillet or wok over medium-high heat. Add the cubed tofu and sprinkle with a pinch of salt. Cook for about 5-7 minutes, turning occasionally, until the tofu is golden brown on all sides. Once cooked, remove the tofu from the skillet and set it aside.
In the same skillet, add the remaining tablespoon of vegetable oil. Toss in the sliced yellow onion and sauté for about 2 minutes until it begins to soften. Then, add the shredded carrots, the white parts of the green onions, and sliced cabbage. Stir-fry for an additional 3-4 minutes until the vegetables are tender but still crisp.
Return the cooked tofu to the skillet and pour in the prepared sauce. Toss everything together, ensuring that the tofu and vegetables are evenly coated. Add the cooked noodles to the skillet and gently mix to combine all ingredients. Cook for another 2-3 minutes until everything is heated through.
Remove the skillet from heat and garnish with the green parts of the green onions. Serve your Sriracha Noodles with Tofu hot, accompanied by lime wedges and extra Sriracha sauce on the side for those who love a little more heat!