I start by warming the olive oil in a skillet over medium heat, then toss in the carrots, celery, and onion. I let them cook for about 8 to 10 minutes until they start to soften and smell fragrant. Right at the end, I stir in the garlic, salt, and pepper for just half a minute more.
Once the veggies are ready, I spread them across the bottom of a lightly greased slow cooker. Next goes the rinsed brown rice, followed by the chicken breasts arranged on top. I pour in the chicken stock and tuck in the bay leaf along with the fresh thyme sprigs.
I cover the slow cooker and set it to low for 5 to 6 hours, or high for about 2.5 to 3.5 hours. I always check the chicken a bit early since it can dry out if it overcooks. Once it hits 165°F internally, I pull it out so it doesn't get tough while the rice keeps cooking.
After removing the bay leaf and thyme stems, I place the chicken on a cutting board and let it cool for a few minutes. Using two forks, I shred it into bite-sized pieces, then return all of it straight back into the pot with the rice and vegetables.
The last step is my favorite. I squeeze in the fresh lemon juice and give everything a good stir. If the soup feels too thick, I add a splash of more stock. A quick taste test lets me adjust the salt and pepper before serving it warm.