Start the soup: Set a large soup pot on the stove over medium heat.

Add the olive oil to the pot and let it heat for about 30 seconds, until it looks loose and shiny.

Add the chopped onion to the pot. Cook for 3 minutes, stirring a few times, until it starts to soften.

Add the diced carrots and diced celery to the pot. Cook for 4 minutes, stirring now and then, until the vegetables look glossy and the onion is more tender.

Add the sliced mushrooms to the pot. Cook for 5 to 6 minutes, stirring occasionally, until they shrink down and any water they release mostly cooks away.

Add the sliced garlic and dried thyme to the pot. Stir for 30 seconds, just until the garlic smells fragrant.

Add the rinsed rice to the pot. Stir for 1 minute so the grains are coated in the oil and vegetables.

Simmer until the rice is tender: Pour the chicken broth into the pot.

Add the kosher salt and black pepper to the pot and stir well.

Raise the heat to high and bring the broth to a boil.

Lower the heat to medium-low so the soup gently bubbles. Cook for 15 to 18 minutes, stirring once or twice, until the rice is tender and the broth looks a little fuller from the starch.

Add the shredded rotisserie chicken to the pot. Stir and cook for 2 minutes, until the chicken is hot all the way through.