Preheat your oven to 400°F (200°C).
In a large bowl, combine the ground beef or lamb, breadcrumbs, chopped red onion, minced garlic, parsley, oregano, cumin, salt, and black pepper. Mix until just combined, being careful not to overwork the meat.
Shape the mixture into meatballs, about 1 to 1.5 inches in diameter, and place them on a baking sheet lined with parchment paper.
Drizzle the meatballs with olive oil, then bake in the preheated oven for 20-25 minutes, or until they are cooked through and golden brown.
While the meatballs are baking, prepare your bowl ingredients. In a separate bowl, mix the cooked rice or quinoa with chopped cucumber, cherry tomatoes, sliced kalamata olives, and thinly sliced red onion.
Once the meatballs are done, let them cool for a few minutes before assembling the bowls.
In each bowl, add a generous scoop of the rice or quinoa mixture, followed by 3-4 meatballs. Top with crumbled feta and a dollop of hummus or tzatziki sauce.
Serve immediately and enjoy your Greek meatball bowl!