Prepare the Noodles & Veggies: Cook the rice vermicelli according to the package directions.
Drain thoroughly and rinse under cold water to stop the cooking process and prevent sticking.
Transfer the cooled noodles to a large bowl.
Add the sliced napa cabbage, chopped cilantro, celery, and shallots, then gently toss to combine.
Pan-Fry the Tofu: While the noodles cook, heat the vegetable oil in a medium nonstick skillet over medium-high heat.
Add the cubed tofu and cook for 12 to 15 minutes, turning occasionally, until golden brown and crisp on at least two or three sides.
Remove from the heat and set aside.
Mix the Dressing & Assemble: In a small bowl, whisk together the lemon juice, sugar, sriracha, salt, and minced garlic until the sugar is fully dissolved.
Pour this vibrant dressing over the noodle and vegetable mixture and toss well to coat everything evenly.
Divide the noodle salad among four serving bowls, top with the warm, crispy tofu cubes, and garnish generously with the toasted coconut flakes before serving.