Using a vegetable peeler (a Y-shaped one works best), cut the carrots lengthwise into long, even ribbons; place in a bowl of cold water.
In a large bowl, mix the vinegar, lemon juice, cumin and 1/4 tsp. salt. whisk in the oil. Drain the carrots and dry on a kitchen towel. Add to the dressing; toss. If desired, let sit until slightly softened, about 10 minutes. Add the mizuna and toss lightly; season with pepper. Add the cheese and transfer the salad to plates. Sprinkle with the pumpkin seeds.