Prepare pickled cucumbers. Thinly slice cucumbers and red onion. Combine boiling water with sugar, salt, and rice wine vinegar, stirring until the sugar and salt have dissolved. Add cucumbers and red onion and let sit for 30 minutes.
Make lemongrass coconut rice. Heat 1 tablespoon olive oil in a medium saucepot over medium-high heat. Add minced garlic, minced ginger, and lemongrass. Saute until lightly browned, about 30 seconds. Add jasmine rice and lightly toast, about 1-2 minutes. Add water and coconut milk and bring to a boil. Cover the pot, reduce heat to low, and continue to cook for 15 minutes or until the rice is light and fluffy.
Preheat oven to 400 degrees F.
Toss cauliflower florets with ground ginger, salt, black pepper, and 2 tablespoons olive oil. Spread cauliflower in an even layer on a baking sheet and roast for 20-25 minutes or until fork-tender.
Heat 1 tablespoon olive oil in a small saucepot over medium heat. Add minced garlic, Thai chile, and scallions. Saute for 1 minute, making sure not to burn the garlic. Add soy sauce, brown sugar, fish sauce, and juice of ½ a lime. Simmer until the sauce has slightly thickened, about 2 minutes. Remove cauliflower from the oven and toss with sauce.
Heat 1 tablespoon oil in a large saute pan over medium heat. Add spinach and minced garlic. Saute until spinach has wilted, about 4-5 minutes. Season with salt and pepper.
Assemble cauliflower larb bowls. Scoop rice into 4 bowls and top with cauliflower larb, pickled cucumbers and onions, garlicky spinach, sliced avocado, and fresh herbs. Drizzle any extra sauce from the cauliflower on top and squeeze extra lime juice. Serve immediately.
Notes
You can make the pickled cucumbers up to 3 days in advance.