Grind lemongrass, onion, and garlic in a blender adding a little water if necessary. Remove and add turmeric and pepper.
Heat oil in a pot and stir fry spice paste until fragrant, about 2 to 3 minutes. Add chicken and stir till chicken turns opaque, about 2 minutes. Add water and season with salt. Reduce heat and let simmer for 10 minutes.
Add cauliflower and peppers and continue to cook for another 5 minutes until cauliflower is tender. Turn off heat and stir in lime juice.