Mix boiling water and ground flax seeds together in a bowl; let sit until thickened, about 10 minutes.
Combine flax mixture, soy milk, tofu, and nutritional yeast in a blender; blend on high speed until flax has almost disappeared. Add cornstarch while blender is still running and blend until batter is smooth. Pour batter into a bowl and refrigerate until chilled, about 30 minutes.
Pour some of the batter into a shallow bowl or plate. Dip bread, 1 slice at a time, into the batter until evenly coated.
Heat oil in a skillet over medium-high heat. Cook each dipped bread slice in the hot oil for 5 minutes; flip and cook the other side until lightly browned, 1 to 2 minutes more.