Set a large soup pot or Dutch oven on the stove over medium heat. Add the olive oil and let it warm for about 30 seconds.

Add the chopped onion, diced carrots, and diced celery to the pot. Stir well to coat them in the oil.

Cook the vegetables for 8 to 10 minutes, stirring every few minutes, until they look softened and the onion is translucent.

Add the sliced garlic and dried rosemary to the pot. Stir for 1 minute, just until the garlic smells fragrant.

Add the rinsed lentils to the pot. Stir for about 30 seconds so they are coated with the oil and vegetables.

Pour the vegetable broth into the pot. Add the kosher salt and black pepper.

Raise the heat to high and bring the soup to a full boil.

Lower the heat so the liquid bubbles gently instead of boiling hard. Cook for 22 to 25 minutes, stirring once or twice, until the lentils are nearly tender but still have a little firmness in the center.

Add the drained chickpeas to the pot. Stir them into the broth.

Add the dried orzo to the pot and stir well so it does not settle on the bottom.

Cook for 8 to 10 minutes over a gentle simmer, stirring every few minutes, until the orzo is tender and the lentils are fully soft. If the soup gets thicker than you like, add a small splash of water or broth.

Taste the soup. Add more salt and black pepper if it needs it.