In a small bowl, mix the first six ingredients. Remove 1/4 cup of the mixture to a larger bowl, add beef to the larger bowl and toss to coat. Marinate for 10 minutes.
Cook spaghetti accordingly to package directions, drain.
In a large skillet or wok, add heat vegetable oil and heat. Add the beef mixture and stir-fry until no longer pink, about 2-3 minutes. (may have to cook in two batches if skillet or wok is not large enough). Remove beef to a plate to keep warm.
Stir-fry water chestnuts, purple onions, and snow peas in oil for 1-2 minute until crisp-tender. Add spinach and hoisin mixture, toss to coat and stir-fry until spinach is wilted.
Return beef to skillet, add drained spaghetti and red chile and toss to combine and heat through.
Serve garnished with green onions and/or sliced almonds, optional