Bring a large pot of water to a boil, and salt the water if desired. Add noodles and cook for the time specified on the package, then immediately rinse under cold water to stop the cooking.
In a small bowl, mix the soy sauce, rice vinegar, coconut sugar, peanut butter, and cornstarch together to make the pad thai sauce.
Heat a large frying pan over medium-high heat, then add olive oil, followed by the onion. Cook until softened and starting to brown, about 5 minutes.
Next, add garlic, tofu, red pepper and the rest of the veggies, and cook for another 2 minutes, stirring frequently.
Add the cooked noodles, sauce, and cashews to the mix. Toss and cook for another couple of minutes until everything is heated through. Squeeze fresh lemon over top and serve hot.