Preheat the oven to 375 degrees Fahrenheit and caramelize the onions and mushrooms in a sauté pan on low heat with the vegan butter.
Mix up the chickpeas and sweet potato in a food processor.
Combine the mash with olive oil and spices in a mixing bowl.
Add the oatmeal (this is important to bind your burger, so it doesn't fall apart, don't deem this step irrelevant and skip it, or you'll have a sad mashed potato on a bun).
Place a foil lining on a baking sheet and coat with a light layer of non-stick cooking spray.
Mould the sweet potato and chickpea mash into patties and place them evenly spaced on the baking pan.
Bake the veggie burgers for 15 minutes, then flip and bake for 10 minutes.