Slice the red onion thinly into rings. Marinate in 1/4 cup of lemon juice. Cover and refrigerate for at least 30 minutes.
Peel and remove pith from both the blood and naval orange. Slice crosswise into 1/4-inch rounds.
Cut the avocado in half crosswise and remove the pit. Peel, then slice crosswise into 1/4-inch rings.
Arrange the orange and avocado slices on a serving dish. Top with baby arugula and pomegranate seeds. Drizzle pomegranate molasses, avocado oil, and lemon juice. Season with salt and pepper as desired.
