Set a large soup pot on the stove over medium-high heat.

Add the olive oil to the pot and let it heat until it looks loose and shiny, about 30 seconds.

Add the sliced fennel to the pot. Cook for 2 minutes, stirring a few times, until it starts to soften.

Add the cauliflower florets to the pot. Season with salt and black pepper.

Cook the fennel and cauliflower for 6 to 8 minutes, stirring every minute or two, until the vegetables have browned spots and the fennel looks slightly tender.

Add the sliced garlic to the pot. Stir for 30 seconds, just until it smells fragrant.

Pour the vegetable broth and 1 cup water into the pot. Use a wooden spoon to scrape up any browned bits from the bottom of the pot.

Raise the heat to high and bring the broth to a boil.

Lower the heat to medium so the broth bubbles gently. Cook for 6 minutes, until the cauliflower is tender when pierced with a fork.

Add the rice noodles to the pot. Press them down into the broth as they soften.

Cook the noodles for 3 minutes, stirring once or twice so they separate and do not stick together.

Add the spinach to the pot in two handfuls, stirring after each addition until the leaves wilt into the broth.