Heat 1 tablespoon neutral oil in a deep skillet over medium heat. Once hot, add the onion and zucchini and cook over moderate heat. Be careful not to brown them too much.

Season the onion and zucchini liberally with salt. Add the sesame oil and minced Thai chili peppers and stir to combine.

Reduce heat to medium-low and let it bubble for 20 minutes. Stir the sauce occasionally to prevent it from sticking. And adjust heat as necessary if it reduces too quickly.

After the zucchini is very tender, add 1 1/2 cups water and bring it to a boil. Reduce heat and simmer an additional 10 minutes until thickened.

Add the minced Thai basil and simmer for an additional 5 minutes—taste and season more to your preferences.

While the sauce cooks, prepare the noodles according to package instructions. If using mung bean vermicelli, place them in a large, heat-proof bowl. Bring 6 cups of water to a boil and pour over the noodles. Let stand for 2–4 minutes until tender. Drain and rinse thoroughly.

Drizzle the noodles with 1 teaspoon sesame oil and toss to coat. Divide between shallow bowls. Pile the warm zucchini sauce on top and mix with tongs or a fork to incorporate. Garnish with a few other Thai basil leaves and shichimi togarashi if you like.