Heat oven to 425°F. Toss potatoes with 1 tablespoon oil and 1/2 teaspoon salt on sheet; roast 25 minutes, turning once, until almost tender.
Reduce oven to 375°F; oil 9-inch square dish with remaining oil. Spread potatoes and squeezed spinach inside.
Blend tofu, soy milk, chickpea flour, nutritional yeast, mustard, garlic powder, paprika, turmeric, pepper, and remaining salt thick and smooth.
Fold tofu mixture through vegetables; level top. Bake 35 to 40 minutes until edges firm and center 165°F.
Rest 15 minutes to finish setting flour and tofu; cut eight portions.