In a large pot of lightly salted boiling water cook the cauliflower florets for 5 minutes or until just tender.
Heat a large wok or cast iron skillet with the extra-virgin olive oil over medium heat. Add in the garlic, ginger, onion, bell pepper, oyster mushrooms, zucchini and snow peas, and stir-fry all the veggies for 2 minutes.
Add in the Thai green curry paste and sugar and cook for another minute.
Drain the cauliflower florets and fold them together with the peas into the pan with the other veggies, and cook for 5 more minutes.
Pour in the coconut milk and tamari sauce, and add in the lemongrass. Cook for 5 minutes, then remove the lemongrass. If the curry is too thick, add a splash of water, and adjust seasoning to taste.
Remove the pot from the heat, squeeze half lime over the top, and sprinkle the fresh coriander and red chilli (if using) all over the curry. Serve with your favorite steamed rice.