Heat the oven to 425°F with a bare rimmed sheet pan on the middle rack. Put potatoes in a saucepan, cover with cold water by 1 inch, add cooking salt and simmer for 7 to 8 minutes after the water begins bubbling, until the outside softens but the center still resists slightly.
Drain potatoes well and let steam escape for 3 minutes. Toss gently with oil, seasoning salt, oregano, garlic powder and pepper.
Carefully arrange the potatoes cut-side down on the hot pan with space between them. Roast without turning for 25 minutes.
Turn the potatoes and roast for 5 to 10 minutes more until fully tender and deeply golden underneath.
Transfer to a bowl, toss lightly with lemon zest and juice and serve immediately while the browned surfaces are still crisp.