Preheat the oven to 425F (220C). Line a baking sheet with parchment paper.
Mix the flour, plant-based milk, salt, pepper, and garlic powder together in a bowl to form a smooth batter. If the batter is a bit too thick, add a splash more milk, if the batter is a bit too thin, mix in a few more tablespoons of flour.
Dip each piece of cauliflower into the batter. Allow any excess batter drip off, then place the cauliflower onto the baking tray. Place the tray into the hot oven and bake for 25-30 minutes, until golden brown. Turn the cauliflower over halfway through the cooking time.
Mix all the sauce ingredients together in a small bowl until smooth and creamy.
Place the cauliflower in a serving dish and drizzle with some of the sauce. Top with sliced green onions and sesame seeds and serve with the remaining sauce on the side.