Heat the olive oil in a large pot over high heat, and sauté the onions until they start to soften, about 5 minutes. Add in the garlic and stir for one more minute.
Add in the coconut milk, curry powder, tamari, maple syrup and salt and whisk well to combine. (Since curry powders can vary by brand, feel free to start with only 3 teaspoons and add more to your taste.)
Taste the sauce and adjust any other flavors as needed (keep in mind that the addition of veggies will dilute the saltiness), then bring the sauce to a simmer and add in the chopped sweet potatoes. Cover the pan, and allow the sweet potatoes to steam in the sauce for 5 minutes.
Remove the lid and add the rest of the vegetables, since non-starchy vegetables will cook faster than the sweet potatoes. Stir the vegetables to coat them in the sauce, then cover the pot again. Lower the heat and cook until the sweet potatoes and vegetables are fork-tender, about 8 to 10 more minutes.
Serve the vegetables and curry sauce over cooked rice, quinoa, or cauliflower rice. Leftover curry can be stored in the fridge for up to 4 days.
*When using canned coconut milk, I like to use this brand since it's BPA-free. You can also make your own coconut milk, if you prefer, by blending together the water and meat of a fresh young Thai coconut. (The type with a shaved white exterior.) There's no need to strain this type of homemade milk, since you want it thick like the canned version. One can of coconut milk is the equivalent of 1 3/4 cup fresh coconut milk.