In a large heavy-bottomed pot (such as a Dutch oven), warm 2 tablespoons oil. Add 1 chopped large yellow onion, 2 chopped celery stalks, and 2 large carrots and stir to coat in oil. Add a big pinch of salt.
While they start cooking, wash and destem 1 pound of mushrooms. Smash them with your hands as you add them to the pot to create big, uneven chunks of mushroom.
Continue cooking this veggie mixture until all of the mushrooms have released all of their liquid and it has evaporated, about 10 minutes.
Use a microplane or the smallest hole of a box grater to grate a 2-inch piece of peeled ginger and 6 garlic cloves, and spoon 2 tablespoons of red curry paste directly into the pot. Add 1 tablespoon yellow curry powder, 2 teaspoons ground cumin, and 1 teaspoon ground turmeric and stir it in for 30 seconds to 1 minute, until fully incorporated and very fragrant.
Stir in 4 cups chicken stock, 1 can coconut milk, 1 cup white rice, 2 pounds chicken thighs, 2 tablespoons soy sauce, 1 tablespoon fish sauce, and 1 tablespoon rice vinegar.
Bring to a boil over high heat, then reduce to a simmer and cover for 10 minutes. Stir in the finely chopped bell peppers and continue cooking for another 5 to 10 minutes, until the rice is tender and the chicken shreds easily when pulled with a fork.
Transfer the chicken to a cutting board and use two forks to shred into tiny pieces. Return the chicken to the pot. Taste for seasonings and adjust salt and pepper as needed. Want it spicier? Add sriracha! Want it tangier? Add more fish sauce and rice vinegar.
If your soup is too thick for your liking, stir in more chicken stock or just water. It will continue to thicken up in the fridge, so I recommend adding a splash of liquid when you reheat it.
Enjoy!