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