Make the Chickpea-Walnut Taco Crumbles according to the recipe for that component and set aside.
Bring a large pot of salted water to a boil and cook the 12 oz spaghetti until al dente according to package directions; drain in a colander, rinse with cool water to stop cooking, then drain very well.
While the pasta cooks, finely dice the onion and mince the garlic.
Heat an extra-large skillet over medium-high. Add the diced onion and sauté 6–7 minutes using 1–3 Tbsp water or vegetable broth for a no-oil method, adding a splash more if needed, until softened.
Add the minced garlic to the skillet and cook 1–2 minutes until fragrant, then reduce the heat to medium-low.
In a small bowl, mix the tomato sauce, dairy-free milk, nutritional yeast, and tamari until smooth to make the creamy tomato sauce.
Add the creamy tomato sauce, the 15 oz diced tomatoes (with juices), and 2 Tbsp tomato paste to the skillet; stir and gently simmer 5–7 minutes to combine and thicken slightly.
Add the drained spaghetti and the prepared chickpea-walnut taco crumbles to the skillet; toss thoroughly with tongs until everything is well combined and heated through.
Turn off the heat and stir in 2–3 Tbsp chopped fresh cilantro if using. Serve with desired optional toppings such as olives, red pepper flakes, vegan cheese shreds, pickled jalapeño, or vegan sour cream.