Fill a medium saucepan half full with water and bring to a boil. Stir in the rice and return to a boil. Simmer, cooking uncovered, until the rice is tender (about 14 minutes). Drain the rice in fine mesh strainer and then transfer to a medium bowl.
While the rice is cooking, mix the red onion and vinegar in a small bowl. Let sit for 5 minutes; then strain the onion through the strainer and discard the vinegar. Set the onion aside.
In a small bowl, whisk together the lemon juice, oil, garlic, salt and pepper. Drizzle this mixture over the hot rice. Mix in the onion, dill and zest. Toss to combine and serve while warm.