Heat oil in a pot. Add chopped shallots, galangal, lemongrass, and red Thai chilies. Saute on medium heat, stirring frequently.
Now add vegetable stock and kaffir limes. Boil uncovered for 15 minutes on medium to high heat. This step will bring out all the flavors from the aromatics.
Now switch off the flame and strain it through a mesh strainer. Discard all the aromatics and keep the stock aside.
Take a pot, add coconut milk, prepared stock, tofu, mushrooms, bell pepper, and carrots. Turn on the flame.
Cook everything on medium heat for 10 to 15 minutes or until all the vegetables are slightly tender.