Cook the pasta. Bring a large pot of water to a boil over high heat. Season with 2 tablespoons salt. Add the spaghetti and stir to ensure that the pasta does not clump together. Boil until just al dente, 6 to 7 minutes. Reserve 1 cup of the pasta cooking water and drain the noodles. Rinse the chickpea noodles under cold water until completely cool. Set aside.

Make the sauce. Meanwhile, heat a large saucepan over medium-high heat. Add 2 tablespoons of olive oil and swirl to coat. Add the garlic, red pepper flakes, and onion powder, if using. Saute, stirring, until the garlic is fragrant, 30 seconds to 1 minute. Do not let brown. Add the cherry tomatoes and dried herbs, if using, and season with salt and pepper. Continue cooking until the tomatoes begin to break down, 4 to 5 minutes. Add the tomato paste and harissa paste and cook for 3 minutes more. Taste the sauce and season with salt, pepper, and additional harissa paste, if desired. (The pasta sauce can be made up to 3 days in advance. Store, covered, in the refrigerator before heating in a skillet.) 

Serve. Add the pasta to the sauce, along with 1 to 2 tablespoons of pasta water to thin, if necessary. The sauce should be thick and concentrated, but just loose enough to coat the noodles easily. Cook for 1 minute more, tossing to combine. Add the chopped basil, gently fold to combine, and divide among serving plates. Serve immediately, topping each portion with a drizzle of olive oil and additional basil.