Marinate chicken with olive oil, oregano, and half the lemon juice for 15 minutes.
Bring chicken broth to a boil in a medium saucepan, stir in couscous, cover, and remove from heat; let stand for 5 minutes.
Heat a large skillet over medium-high heat and cook marinated chicken until golden brown and internal temperature reaches 165 degrees Fahrenheit.
Fluff couscous with a fork and divide equally among four serving bowls.
Arrange cooked chicken, cucumber, tomatoes, red onion, olives, and feta cheese over the couscous base.
Drizzle with remaining lemon juice and serve each bowl with a dollop of tzatziki sauce.