Process all the ingredients in a food processor. Drizzle in some water if necessary.
In the large skillet, warm the olive oil over medium-high heat and sauté the onions until soft, about 2 to 3 minutes. Add the mushrooms and sauté until tender, not mushy, about 5 to 6 minutes. Stir in the curry paste and cook for 1 more minutes. Transfer to the slow cooker.
Add all the vegetables, the vegetable stock, and the salt. Set the slow cooker for low and allow to cook for 4 to 5 hours, until the vegetables are fork tender, but not mushy. During the last 30 minutes of cooking, stir 1/2 cup of the broth from the slow cooker with the coconut milk. This will help bring up the temperature of the curry and reduce or prevent curdling. Stir I the coconut milk mixture and cover. Check the temperature after 15 to minutes, and serve when it’s hot to your taste. Leftovers will keep in the refrigerator for 3 days, and up to 1 month in the freezer.