Preheat the oven to 400°F.
In a large bowl, toss the sliced carrots with olive oil, salt, pepper, and cumin until evenly coated.
Spread the carrots in a single layer on a baking sheet. Roast in the preheated oven for 25-30 minutes, or until tender and slightly caramelized, stirring halfway through.
In a large mixing bowl, combine the cooked lentils, red onion, parsley, and roasted carrots once they are done.
Drizzle the lemon juice over the mixture and toss gently to combine.
Serve the salad on a plate or in a bowl, topped with a dollop of hummus and crumbled feta cheese, if using.