Heat the oven to 425 degrees F. Scrub and dry the sweet potatoes and prick each one four or five times with a fork.

Rub with the olive oil and kosher salt and set them directly on the oven rack with a sheet pan on the shelf below.

Roast 45 to 55 minutes, until a skewer slides into the center with no resistance. Do not microwave them, roasting gives drier, sweeter flesh.

Put the sliced cremini in a 12 inch skillet over medium-high heat with NO oil. They will squeak, then release their water and sit in a shallow pool for 4 to 5 minutes.

Once the water has boiled off and the mushrooms sizzle, add the olive oil and cook 3 to 4 minutes more, stirring rarely, until the edges are deeply brown.

Add the onion and cook 4 minutes until soft. Stir in the garlic, cumin, smoked paprika, oregano and thyme for 30 seconds, then scrape everything to the outer edge of the pan.

Add the ground turkey to the cleared center, press it flat and leave it undisturbed for 4 minutes. Break it into chunks, stir through the mushrooms and cook 4 minutes more until no pink remains.

Season with the salt and pepper only now, at the end. Salting early draws water out of the meat and poaches it.

Add the spinach in two handfuls, letting the first wilt before adding the second, about 2 minutes total.

Push everything to one side, tilt the pan, and let the green liquid that collects bubble away for 1 to 2 minutes, or spoon it off.

Off the heat, stir in the soy sauce and lemon juice. Taste and adjust, the filling should be slightly more assertive than seems right.

Split each roasted potato lengthwise without cutting through, open it like a book, fluff the flesh with a fork, and divide the filling among the four.