Add all the ingredients from white beans through lemon juice to a blender or food processor, then add 1-2 tbsp of the water. Blend, scraping down the sides as needed, until combined. It should be very thick.
Continue to add water by the tablespoon, blending after each addition, until the hummus is the consistency you like. If you prefer chunkier hummus, use the pulse function on the food processor and process until just combined.
Taste the hummus and add salt, pepper, and za'atar to your preference. Za'atar has some salt in it, so if you use more za'atar you won't need as much salt (and vice versa).
Add the hummus to a bowl and top with extra olive oil and a sprinkle of za'atar. Serve the carrots alongside the hummus for dipping, or dollop the hummus on top of the carrots.