Heat oven to 400 degrees. Wrap beets in foil and roast until tender, about 1 hour. Let cool, then peel and dice.
Whisk together olive oil, lemon juice, honey, garlic, and fennel and caraway seeds. Season with salt and pepper. Toss with beets.
For each serving, toss 1 cup dressed beets with 1 cup spinach and 1/4 cup parsley. Season with salt and pepper and top with onion.
Refrigerate marinated beets in an airtight container up to three days.