Set the oven to 425°F. Lightly grease an 8x8-inch baking dish or line it with parchment paper.
In a small saucepan over low heat, whisk the cornstarch and water until smooth. Stir in the sugar, tamari, vinegar, garlic, ginger, and black pepper. Let the sauce simmer, stirring often, until it thickens.
Place the chicken-style pieces in the baking dish in a single layer.
Brush the glaze over the pieces, flip them, and brush again to coat both sides.
Bake for 30 minutes, brushing with more glaze and turning the pieces every 10 minutes.
Serve hot with rice, noodles, or roasted vegetables.