Add the beans to a large pot. Cover with more than 3 inches of water, bring to a boil, and then reduce to a simmer. Simmer for 45 minutes to 1 hour, tasting after 45 minutes to get the desired tenderness.

Fill a separate large pot with enough water to cover the beets and bring to a boil. Add the beets and cook for 45 minutes to 1 hour, checking after 45 minutes to reach the desired tenderness.

In separate pots, boil the carrots and sweet potatoes for 30 minutes each until their skins easily come off with a fork or knife. Drain the vegetables and refrigerate them or let them sit in an ice bath until chilled.

Peel the skin from the beets, sweet potatoes, and carrots, and finely dice them into even cubes.

In a separate pot, boil the frozen peas for 6 to 8 minutes. Drain and cool to room temperature.

In a large mixing bowl, add all the vegetables, oil, vinegar, and salt to taste. Mix to combine.

Allow the ingredients to sit together for at least 2 to 3 hours (or overnight). Serve topped with the green onion.