Heat your BBQ to 400 degrees. If you don't have a BBQ, just use your oven, and place your eggplants on a parchment-lined baking sheet.
Cut the eggplant in half length-wise and rub all over with 1/2 to 1 tbsp olive oil. Brush the 1/2 lemon and the garlic bulb with a little olive oil as well.
Roast the eggplant, lemon and garlic on your hot BBQ for about 15-20 minutes. Place the eggplant on the hottest part of the BBQ, but put the lemon and garlic up on the side where it's not quite as hot.
Once the eggplant is roasted and soft, remove from the BBQ or oven and place in a zip-top bag for a few minutes to cool. This will help the skin to peel off easier.
Once the eggplant is cool enough to handle, strip the inner flesh off of the skin.
Place the eggplant flesh in the blender, then juice in the lemon. Pull 2-3 the roasted garlic cloves out of their paper husks and add as well.
Add the salt, spices, and tahini.
Blend, pulsing at first, to get everything mixed. Then, with the blender running, slowly add in the last 2 tablespoons of olive oil.
Stop the blender and scrape down the sides. Taste for seasoning and adjust. Blend one more time.
Serve with a drizzle of olive oil on top, and a sprinkle of fresh herbs and za'atar. Serve with bread and raw vegetables to dip.