Position a rack in the upper third of the oven; preheat to 400 degrees . Line a baking sheet with foil; coat with cooking spray. Combine panko breadcrumbs with the milk. Let sit for 5 minutes.
Combine the breadcrumbs, ground turkey, scallions, soy sauce, water chestnuts, garlic, egg, 1 tsp. salt and 1/2 tsp. pepper. Shape into a 5-by-8-inch rectangle on the sheet.
In a bowl, stir together the ketchup, brown sugar and chili paste; spoon half of the mixture over the loaf, spreading to cover. Bake, coating with the remaining glaze halfway through, until a thermometer inserted in the center registers 165 degrees , 1 hour. Let rest for 10 minutes before slicing.