In a large pot over medium heat, warm the oil. Add the cauliflower, chickpeas, garlic, 1 teaspoon salt, pepper, and red pepper flakes (if using).
Cook until very fragrant and the cauliflower has softened a bit, about 5 minutes, stirring occasionally. Towards the end of cooking, use the back of a fork to mash up some of the chickpeas (this will help thicken the sauce).
Stir in the water, pasta, rosemary, and remaining 1 teaspoon salt. Scrape the bottom of the pot in case anything is stuck on there.
Bring to a boil over high heat and give it a stir, scraping the bottom of the pot in case anything is stuck (continue to do this whenever you stir!). Reduce the heat to medium-high to maintain a rapid simmer for 15 minutes, or until the pasta is cooked through and the liquid/sauce is starchy and thick, stirring occasionally. The pasta is meant to be very saucy, but not a watery soup. It will thicken up a bit as it cools down.
If the pasta is still not cooked through and the water is very low, just add more hot or boiling water and continue to cook until the pasta is done to your liking. If you have too much water and pasta is cooked, increase the heat and boil some of the liquid off.
Serve topped with plenty of parm, black pepper, a generous drizzle of good olive oil, and a squeeze of lemon. If you have fresh parsley, that’s also nice on top.