In a small bowl, mix warm water, warm milk, yeast, and 1 tbsp sugar. Let sit for 5-10 minutes until frothy.

In a large bowl, whisk together flour, remaining sugar, baking powder, and salt. Add the yeast mixture and 1 tbsp oil. Knead for 8-10 minutes until smooth and elastic.

Place dough in an oiled bowl, cover, and let rise in a warm place for 1 hour or until doubled in size.

Punch dough down, divide into 10-12 pieces. Roll each into a ball, then flatten into an oval shape.

Brush the top of each oval lightly with oil. Fold in half crosswise (like a taco) and place on a small square of parchment paper.

Set up a steamer over boiling water. Steam the buns in batches for 10-12 minutes. Turn off heat and wait 3-5 minutes before opening the lid to prevent collapsing.

While buns steam, toss chicken strips in cornstarch. Pan-fry in oil over medium-high heat until crispy. Whisk soy sauce, hoisin, brown sugar, garlic, and ginger, then pour over chicken. Simmer until sauce is thick and sticky.

Assemble buns by gently opening the steamed bao, adding a few slices of cucumber, the sticky glazed chicken, and topping with scallions and sesame seeds. Serve immediately.