Combine spices in a bowl. Place potatoes in a pot of cold water, add salt, and cook until potatoes are tender but firm, about 10 minutes. Drain, let cool, and cut each potato lengthwise into 8 slices. Heat grill to high. Brush potatoes w/ oil, season w/ the spice rub, and grill until golden brown and cooked through, about 3 to 5 minutes.