Preheat the oven to 400°F.
Arrange the onions on a sheet pan, toss with 1 tablespoon olive oil and a pinch of salt. Roast until lightly browned, 12-15 minutes.
Place the carrots for the hummus in a medium saucepan, cover with water and add a pinch of salt. Bring to a simmer and cook until the carrots are fork-tender, about 10 minutes. Drain.
Place the roasted onions, cooked carrots, pine nuts, harissa, cumin and lemon juice in a food processor and blend until smooth. Combine the water and remaining oil in a glass measuring cup and pour into the food processor, with the motor running. Blend until smooth. Season with salt and pepper.
Toss the remaining carrots on a baking sheet with enough olive oil to coat, za’atar and salt. Roast until tender and lightly browned, about 10 minutes.
To serve, spread spicy carrot hummus on a serving platter. Arrange carrots on top and garnish with feta, cilantro and pine nuts.