Preheat oven to 425° F.
Heat oil in a large oven proof skillet (preferably cast-iron) over medium heat. Add onion and cook, stirring, until beginning to brown, about 4 minutes. Add spinach and garlic; cook, stirring, for another minute. Remove from heat and let cool slightly. Add rice, feta, dill, pepper and salt to the pan; stir to combine.
Whisk eggs, sour cream and lemon zest in a medium bowl. Add to the rice mixture and stir well to combine. Smooth the top with a rubber spatula. Bake until lightly browned in spots, about 25 minutes. Let stand for 5 minutes before serving.