Preheat oven to 400F/200C. Chop sweet potatoes into bite-sized cubes. Line a baking tray with parchment paper and spread sweet potatoes onto tray. Drizzle with oil and toss to coat. Cook for 20 mins. (Keep oven on for later).
Meanwhile, toss onion, garlic, red bell pepper, and 1 tbsp neutral oil into a large deep skillet (or saucepan) on medium-high heat. Cook, stirring often until veg is softened (approx. 10 mins). Then add cumin, sea salt, chili powder and cinnamon. Toss to combine.
Drop in spinach and cook for a few minutes until wilted. Finish by dropping in roasted sweet potato and black beans. Stir to combine. Remove from heat.
Assemble enchiladas by pouring 1/4 cup of the homemade enchilada sauce into your casserole dish. (I used a 8.5 x 11 inch baking dish). Spread out the sauce to coat the base.
Grab a tortilla and add spoonfuls of filling mixture to the middle. You want it full, but not too full that you can't roll it (about 1/2 cup of filling should do). Snugly fold in the sides to form a log. Place the burrito seam side down into your casserole dish. Repeat with remaining tortillas and filling, until you've used them all up and the tortillas are snug in the casserole dish,
Drizzle the top of your pan with remaining homemade enchilada sauce. Spread to cover as best you can. Cook enchiladas for 20 mins, or until the top is golden and bubbling. Let cool slightly (approx. 10 mins) before serving.