Season the lamb with salt and pepper. In a large pot, heat the oil over medium-high heat, then brown the lamb on all sides, about 6 minutes in all. Transfer the lamb to a plate with a slotted spoon.
Add the onions and garlic to the same pan and sauté for about 5 minutes over medium heat until the onions are tender and lightly golden.
Add the ginger, coriander, cinnamon, and red pepper flakes to the pot and stir so that the onion is coated with the spices.
Add the tomatoes and the water, return the lamb to the pot, and bring to a simmer over medium-high heat. Reduce the heat to medium-low, cover the pot, and keep it at a low simmer for about 2 hours, until the lamb is almost tender. Add the squash and simmer for another 45 minutes until the lamb is very tender and the squash is cooked through.
Sprinkle over or stir in the parsley and serve hot.
Notes
If you are one of those people who think stews are tricky, 9/10 times it's because you just haven't cooked the meat long enough or kept the temperature low enough. Most stews call for cuts of meat that are very tough when cooked quickly or at too-high temperatures, and there's no amount of seasoning or wishing that can change that. Low and slow, low and slow.
To add flavor and texture, sauté the meat in a hot pan with olive oil before you start adding liquid and braising the meat.
I sometimes use ghee instead of olive oil — a bit of a buttery flavor is added, but the smoking point remains high, so the pan won't start to smoke. Ghee is lactose-free, so you won't have any issues on that front.
You can stir the parsley into the stew at the end, sprinkle the parsley on top of the whole thing, or just on the portions of those who don't have issues with green flecks in their food.
Find yourself a great-looking pot to cook this in so you can plunk it down on the table and save yourself washing a serving bowl.