In a large bowl, toss the potatoes with the 3 Tbsp olive oil, salt, pepper, cumin and ginger. Tip into a lightly greased roasting pan and spread into one layer. Bake until the potatoes are fork-tender and golden brown, about 25 to 35 minutes.
Meanwhile, add the pumpkin seeds to a cold skillet and cook over low heat, stirring, until toasted. Transfer the seeds to a small bowl, toss with 1 tsp olive oil and season with salt and pepper. Set aside.
Dressing: Prepare the dressing by combining all the ingredients (except for the olive oil) in a small saucepan and heating on low until just lightly bubbling. Remove from heat and whisk in the olive oil.
Assemble salad by gently tossing the roasted potatoes with the cranberries and scallions. Add about half the dressing, or enough to coat and garnish with toasted pumpkin seeds. Serve with extra dressing on the side.