Slice each tofu square diagonally to make 8 triangles. Make a cut into the base of each tofu triangle and scoop out enough of tofu to create a pocket.

Combine scooped-out tofu pieces, prawns, egg, ground chicken, green onion, cornstarch, sesame oil, salt, and pepper in a bowl for the filling. Carefully stuff filling back into the tofu triangles; the filling will bulge out.

Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add stuffed tofu triangles, cover, and steam for 20 minutes.

Meanwhile, make the batter. Mix egg and flour in a bowl. Whisk in enough water to give batter a medium-thin consistency.

Combine water, peanuts, red chile pepper, garlic, vinegar, salt, and sugar in a bowl. Stir until salt and sugar have dissolved and set sauce aside.

Remove cooked tofu triangles from the steamer.

Heat oil in a wok until hot. Dip triangles into the batter and slowly lower into the hot oil. Fry in batches until golden brown and the batter is cooked through, about 5 minutes. Drain on paper towels. Serve hot with the peanut sauce.