Build the base: Set a large soup pot or Dutch oven over medium heat.

Build the base: Add the olive oil to the pot and let it warm for about 30 seconds.

Build the base: Add the chopped onion, diced carrots, and diced celery to the pot. Sprinkle in 1/2 teaspoon of the salt and cook for 5 minutes, stirring a few times, until the vegetables start to soften.

Build the base: Add the butternut squash to the pot. Cook for 4 minutes, stirring now and then, until the edges look a little glossy and the squash starts to soften.

Build the base: Add the sliced garlic and chopped rosemary to the pot. Stir for 1 minute, just until they smell fragrant.

Build the base: Add the rinsed lentils to the pot and stir them through the vegetables for about 30 seconds.

Simmer the stew: Pour the vegetable broth into the pot. Add the drained chickpeas, the remaining 1 teaspoon salt, and the 1/2 teaspoon black pepper.

Simmer the stew: Turn the heat to high and bring the liquid to a boil.

Simmer the stew: Lower the heat to medium-low so the liquid bubbles gently. Cover the pot partway with a lid and simmer for 20 minutes.

Simmer the stew: Uncover the pot and stir the stew well, making sure nothing is sticking on the bottom.

Simmer the stew: Keep simmering the stew for 8 to 10 minutes more, until the lentils are tender and the squash is very soft when pressed with a spoon.

Finish the pot: Use the back of a wooden spoon to mash some of the squash and a few chickpeas against the side of the pot. Stir them back in to thicken the broth.