Warm the remaining 2 tablespoons of coconut oil/olive oil in a large saucepan over medium heat. Add onion, carrots, celery, if using, salt and pepper, red pepper flakes and oregano/thyme/marjoram, if using. Sauté for 7 minutes, until the vegetables soften up. Add the mushrooms and sauté for another 8 minutes, until the water released by the mushrooms evaporates and they begin to brown. Add garlic and stir around for another minute.