Put an oven rack about 6 inches from the broiler and heat the broiler to high. Set a rimmed sheet pan on the counter.

Put the cauliflower florets on the sheet pan. Add the sliced red bell pepper to the same pan.

Drizzle 1 tablespoon of the oil over the vegetables. Sprinkle them with 3/4 teaspoon of the salt and 1/4 teaspoon of the black pepper.

Toss the vegetables on the sheet pan until coated, then spread them into a single layer so the broiler can brown them evenly.

Slide the sheet pan under the broiler. Broil for 6 to 8 minutes, until the pepper starts to blister and some cauliflower edges turn dark brown.

While the vegetables broil, set a large soup pot on the stove. Add the remaining 1 tablespoon oil and place the pot over medium heat.

Add the scallion whites to the pot. Cook for 1 minute, stirring a few times, until they start to soften.

Add the sliced garlic to the pot. Cook for about 30 seconds, stirring, until it smells fragrant but is not browned.

Pour the vegetable broth and tamari into the pot. Turn the heat to high and bring the broth to a boil.

Pull the sheet pan from the oven and stir the vegetables. Return the pan to the broiler for 2 to 4 minutes, until the cauliflower is just tender and more edges are charred.

Squeeze the juice from one lime half into the pot. Lower the heat so the broth stays at a steady simmer instead of a full boil.

Add the rice noodles to the pot. Press them down into the broth and stir gently after 1 minute to separate the strands.