Pre-heat your oven to 400 degrees. Line a baking sheet with parchment paper
Place the cubed sweet potatoes on the prepared baking sheet and drizzle with 2 tsp avocado oil. Sprinkle with cinnamon and a pinch of salt and toss to coat. Roast the sweet potatoes for 25 minutes, turning once halfway through the cooking time, until tender and lightly browned. Reduce oven to 375 degrees.
Heat a tbsp of avocado oil in a large saucepan over medium heat. When hot, add the onion and garlic. Cook for 3 minutes until the onions are translucent and the garlic is fragrant. Add the cumin and paprika and cook for one more minute until the spices are nice and toasty. Transfer the mixture to the bowl of a food processor and set aside
In the same saucepan, heat the remaining tbsp avocado oil over medium heat. When hot, add the chopped spinach and a pinch of salt and cook for 4-5 minutes until wilted and tender. Transfer to the food processor bowl with the onions. Pulse for a couple of seconds until well combined but not a paste
Add the roasted sweet potatoes and black beans to a large bowl. Mash until the end result is quite smooth but still with some chunks. Add in the feta cheese, cilantro, onion mixture and almond meal. Stir to combine.
Line a 1/3 cup measuring cup with plastic wrap and a baking tray with parchment paper. Fill the lined measuring cup with the sweet potato mixture and push down lightly to ensure the burger will stay together. Lift out and transfer to the prepared baking sheet.
Pop the burgers in the oven for about 35 mins, flipping after 20 mins to ensure even cooking.
Serve on fresh bread, buns or lettuce leaves with sliced avocado, mayo, red onion and tomatoes.