I've seen cumin with a pesach hecksher. If you need it for your recipe, I bet you can find it.
That may not have been so helpful, sorry.
I'd probably substitute some cinnamon and a bit of cayenne, but the flavors would be radically different. Cumin has a flavor all it's own.
Here's the recipe and our Rabbi holds that cumin is kitniyot (In the recipe, I substituted raisins for the dried cranberries)
1 cup quinoa, rinsed
1 medium sweet potato, peeled and cut into 1/2-inch cubes, all around rhe same size
3 1/2 tablespoons extra virgin olive oil, divided
1/3 cup pine nuts
4 teaspoons apple cider vinegar
2 teaspoons honey
1/4 teaspoon salt
1/4 teaspoon ground black pepper
1/2 teaspoon ground cumin
1/2 teaspoon cinnamon
1/3 cup dried cranberries
4 scallions, sliced
I know this may be heretical, but I say . . . just leave it out. There's no way you are going to substitute the flavor of cumin, since it's so unique. You can put something else in (like the ginger Adina suggested), or something like allspice or nutmeg, which might go along with the cinnamon already in the dish. But salads are very flexible; as long as there is enough flavor from the various ingredients, I don't see why you have to go crazy trying to substitute for it.