Prepare the tofu by laying the slices out on two layers of paper towels. Top tofu with an additional layer of paper towels and use gentle pressure to wick away any surface moisture. Remove the top layer of paper towels and let the tofu sit for about ten minutes to air dry.
Bring a pot of water to a boil for the noodles. Meanwhile, heat the wok or pan over high heat, and add a tablespoon or two of oil. Add the ground plant meat if using. Add the onion and garlic. Continue to cook over high heat until the onions are slightly softened and browned at the edges. Stir in the spinach until it is just wilted. Season with salt and pepper.
Meanwhile, cook the noodles according to the package directions. Add to a bowl, along with the soy sauce, dark soy sauce, sesame oil, honey, and chili oil (if using). Toss with the onion, meat, and spinach mixture.
To make the sauce, whisk together soy sauce, rice vinegar, sambal, sugar, sesame oil, and water until sugar is completely dissolved. Transfer 1/2 cup of sauce to a small bowl and set aside for serving. Whisk the cornstarch into the remaining sauce mixture and set aside.
Heat oil in a large, non-stick skillet set over medium heat. When oil is shimmering but not smoking, gently lay the tofu in one even layer. Season with salt and pepper and cook undisturbed for 4-5 minutes or until light, golden brown. Flip and cook on the other side until golden brown.
Add the reserved sauce-cornstarch mixture to the tofu. Bring to a boil and then remove from heat. The sauce should thicken very quickly. If it gets too tight, add a splash of water to thin it out. Place on top of noodles and serve.