Rinse the quinoa under cold water and combine with 2 cups of water in a medium pot; bring to a boil, then reduce heat and simmer covered for 15 minutes.
Heat the extra virgin olive oil in a large skillet over medium-high heat and add the ground beef, breaking it into small crumbles with a spatula.
Season the beef with minced garlic, dried oregano, sea salt, and black pepper, cooking until the meat is browned and fully cooked through.
While the beef and quinoa cook, dice the cucumber, halve the cherry tomatoes, and thinly slice the red onion.
In a small bowl, whisk together the plain Greek yogurt, lemon juice, and finely chopped fresh dill to create a refreshing tzatziki sauce.
Remove the quinoa from heat and fluff with a fork, then divide it into four serving bowls.
Top the quinoa with the seasoned ground beef, fresh vegetables, and crumbled feta cheese, then finish each bowl with a generous dollop of the yogurt sauce.