Preheat the oven to 425°F.
Toss the sweet potatoes with the cumin and a drizzle of oil on a baking sheet. Season with salt and pepper. Bake in the centre of the oven, stirring halfway through cooking, until golden-brown, 22-23 min.
While our potatoes are roasting, prepare your fresh ingredients. Cut the cucumber into 1/2-inch cubes. Mince or grate the garlic. and chop the olives (removing any pits). Chop the oregano leaves and zest and then juice the lemons. Set all ingredients aside.
To prepare your meatballs, in a medium bowl combine the beef, garlic, feta and half the oregano. Season with salt and pepper. Roll the mixture into 1-inch round meatballs.
Place the meatballs on a foil-lined baking sheet. Bake in the centre of the oven, until golden-brown and cooked through, 8-10 min. In order to ensure that your meatballs are fully cooked cut one open and be sure that there is no pink inside.
While your meatballs and sweet potatoes are cooking, in a medium bowl whisk together the lemon zest, lemon juice and a drizzle of oil. Season with salt and pepper. Toss in the cucumber, red onion, olives and the remaining oregano. Divide the olive and cucumber salad, roasted sweet potatoes and meatballs between plates. Enjoy!