Preheat oven to 375 degrees F.
Place lentils in small bowl. Cover with cold water & soak for 10 minutes. Drain.
Cook in boiling salted water about 30 minutes, until firm. Drain, rinse under cold water, and drain again.
Place diced squash in large bowl and toss with 2 tablespoons of the olive oil, cumin and sea salt.
Arrange squash in single layer on baking sheet, and roast until tender for 30-35 minutes, turning the squash after about halfway through. Cool.
Combine lentils, squash, and oil from baking sheet with arugula, an additional tablespoon of oil, and red wine vinegar. Season with salt and pepper, and toss.
Divide onto plates, top with feta and serve.