Preheat the oven to 400 degrees* and line a baking sheet with aluminum foil. Toss the cubed butternut squash in 2 teaspoons of the olive oil and sprinkle with salt and pepper to taste. Arrange the squash in a single layer on the prepared baking sheet and bake for 15 minutes. Flip the squash cubes over with a spatula and return to the oven for another 15 minutes.
*While the oven is heating, drizzle the remaining teaspoon of oil in a 5 QT Dutch oven or large pot and bring to medium heat. Add the onions and stir to coat. Saute the onions, stirring occasionally, for a few minutes until softened and translucent. Stir in the garlic and cook for an additional minute until fragrant. Add the farro and stir to coat. Cook for another minute and then add the wine and stir. Allow the wine to simmer until absorbed by the farro.
Add ½ cup of broth and continue to cook, checking and stirring fairly regularly until absorbed. Add an additional ½ cup and repeat ½ cup at a time until all 4 cups of broth are absorbed. In my experience, this will take around 40 minutes total. You don’t have to stir continuously with farro like you would with arborio rice (the traditional risotto base), but you’ll want to stir every couple minutes and check to see if the liquid is absorbed.
When all the liquid is absorbed and the farro is tender and chewy, stir in the thyme, sage, salt and pepper. Reduce the heat to low and add the Parmesan and spinach and stir until well combined. Add the roasted butternut squash from step one and the chopped chicken and stir together. Heat for another minute or two, stirring regularly until spinach is wilted and the ingredients are heated through.