Preheat your oven to 400º.
Prepare a brine solution by combining one quart of warm water with 1 tbsp of salt. Stir until the salt has dissolved, then add the shiitake mushrooms. Place a small bowl or dish over the mushrooms to fully submerge them. Set aside for 10 minutes. See Recipe Notes.
Warm a large stockpot on low heat. Add the coconut oil and heat until shimmering. See Recipe Notes.
Add the lemongrass, scallion whites, fresh garlic and fresh ginger. Stir and cook until fragrant. About 1-2 minutes.
Add the red curry paste and increase the heat to medium. Stir to thoroughly coat the aromatics with red curry paste. Sauté until the red curry paste darkens in color. About 2-3 minutes.
Add the tamari and 1 1/2 quarts of water. Cover and simmer for 20 minutes.
While the broth is simmering, drain the shiitake mushrooms and pat them dry. Then spread them and the broccolini out on a baking sheet. Drizzle with 1 tbsp safflower oil and use your hands to coat the mushrooms and broccolini. Roast the vegetables on the middle rack for ~20 minutes, pausing to toss the vegetables halfway through. See Recipe Notes.
When tossing the roasted vegetables, add the tomatoes to the baking sheet before returning it to the oven.
Retrieve the lemongrass stalks from the broth and discard.
Add the lime juice, sugar and coconut milk to the broth. Simmer for 2-3 minutes to meld the flavors and warm the broth.
Prepare each serving bowl with a serving of pad Thai rice noodles. Add some roasted shiitake mushrooms, broccolini, fresh baby spinach and blistered tomatoes.
Add the broth to each bowl and top with scallion greens, Thai red chilies and sriracha sauce, if desired.