To a food processor, add drained chickpeas, lemon juice, tahini paste, rosemary, salt, and cumin. Pulse the food processor off and on for about a minute or so, until very smooth.
Scrape down the sides, then add about 3/4 of the roasted garlic (set the remainder aside to mince for a garnish). Pulse until well combined.
While the food processor is on, stream in the 2 Tbsp of olive oil.
Add the water, starting with about 2 Tbsp, adding more a little at a time until you get a consistency you're happy with. If your food processor has the ability to stream in liquids as it's running, definitely do that. Otherwise, you can add some water, process it, open the lid, check the consistency, and go from there. (3 Tbsp will yield a slightly thinner hummus, and 2 Tbsp will yield a slightly thicker hummus).
Pulse until desired texture is reached.