Heat the oven to 220C (425F) and line a baking sheet with parchment. Give the parchment a light spray or brush of oil.
Toss the chicken chunks with the egg white, salt, and white pepper until every piece is slick. Add the cornstarch and toss again until the coating looks like a thin batter, not a dusty powder.
Spread the chicken on the sheet in a single layer with space between pieces. Crowded pieces steam instead of crisping. Bake 8 minutes, flip, then bake another 8 minutes until the edges are golden.
While the chicken bakes, stir the honey, soy sauce, rice vinegar, sesame oil, and garlic in a large skillet. Simmer over medium heat for 2 to 3 minutes until it bubbles thickly and coats a spoon.
Tip the baked chicken into the skillet, turn off the heat, and toss until every piece is glazed. The residual heat is enough; boiling the chicken in the sauce softens the crust.
Scatter over the sesame seeds and scallions and serve with rice and steamed greens.