Combine spices in a mixing bowl. Add 1 tablespoon of olive oil and stir to combine. Add seitan to the bowl and toss to coat and pour seitan onto the pan.
Add a half tablespoon of olive oil and the cubed sweet potatoes to the same mixing bowl with a pinch of salt and pepper and toss to combine. Pour onto the sheetpan next to the seitan.
Into the same bowl again, combine onion, pepper, zucchini the remaining ½ tablespoon of olive oil and another pinch of salt and pepper and pour onto the pan.
Place pan into the Foodi oven, set to the Air Roast option, 425* for 15 minutes. After 15 minutes have elapsed, remove the seitan from the pan and into a bowl for serving, toss the sweet potatoes and veggies so they can brown evenly and return to the oven for another 7 minutes.
While in the oven, into a small jar, combine tahini, lemon juice and water in a small jar. Shake to combine. Add a pinch of salt and pepper. Shake once more to combine.
After the 7 minutes have elapsed, remove the pan from the oven, serve in bowls with a generous pour of tahini dressing and a handful of chopped parsley.