In a large bowl, gently toss the tofu cubes with the corn starch and salt until all sides are coated. Also, prepare a paper towel-lined plate for when tofu is cooked and set aside.
Add all the sauce ingredients to a medium bowl and whisk to combine well. Taste and adjust flavor if needed. Set aside.
Cook stir-fry noodles according to package directions. I usually reduce the cook time by 1-2 minutes for firmer noodles. Rinse with cold water and drain well. Drizzle with oil to prevent sticking.
Heat up a Wok or Large Skillet over medium-high heat for 1-2 minutes. Once heated add oil and wait until it shimmers. Now add prepared tofu cubes and let them sit for 1-2 minutes to brown. Using tongs or sturdy spatula, flip to the other side to brown. Continue until all sides are crispy. Remove from heat and place tofu on the paper towel-lined plate. Wipe out wok.
Place the wok back on the stove over medium-high heat. Once heated, add the oil and wait for it to shimmer. Now add the onions and stir fry for 1-2 minutes until slightly softened. Add the optional red pepper flakes.
Now add the peppers and broccoli. Stir fry for about 4-6 minutes until the veggies are crisp-tender.
Turn heat down to medium and add the crispy tofu. Whisk the prepared sauce again and pour into the pan. Cook for 1-2 minutes until slightly thickened. Stir often.
Add the noodles and gently toss to coat. Cook for 1-2 minutes to warm noodles. Remove from heat and serve. See notes for serving ideas.
Video
Notes
* PRESSING TOFU: wrap a block of tofu in a few paper towels and place it on a rimmed plate. Add a cast iron skillet on top (or something equally heavy) and let it drain for 20-30 minutes. Pat dry to remove excess moisture on the surface. You can also use a Tofu Press to make it even easier.* SERVING IDEAS: lime wedges, sriracha, sliced green onion, chopped cilantro, toasted peanuts. toasted sesame seeds.