Wash and rinse the rice until the water runs clear. You can cook the rice in a rice cooker, pressure cooker, or a regular pot. Add the rice to your cooking untensil of choice along with the Thai curry paste. Pour in the coconut milk and 2 ¼ cups of water. Stir gently making sure the curry paste has dissolved.
Cook the rice and set aside to cool completely. Ideally you want to cook the rice a few hours in advance. If this is not possible, leave to cool in the fridge once cooked.
Add oil to a large wok/pot and sauté onions and peppers until the onions are lightly browned. Add mushrooms and sauté for a minute. (If using, add your meat into the wok at this stage. Make sure it's completely cooked through before you add the rice.)
Add the cooled rice to the wok, breaking up any clumps with your hands in the process. Season with lemon juice and fish sauce. Taste and adjust seasoning.
Remove from the heat and stir in the coriander and tomatoes. Serve as is or with a fried egg on top. (note: this rice is quite mild in flavour. I find that it needs some sautéed veg/meat or other side dish on the side to make it a complete meal)