Smoked-Sable Tartare with Beets and Watercress

INGREDIENTS

• 2 1/2 tablespoons fresh lemon juice, or to taste
• 2 bunches watercress, torn into small sprigs (6 cups)
• 1/4 cup finely chopped shallots
• 2 tablespoons white-wine vinegar
• 1/2 pound sliced smoked sablefish (black cod), chopped (about 1 1/3 cups)
• 1/4 teaspoon sugar
• 3 medium beets (about 1 1/2 pound with greens)
• 1/4 cup extra-virgin olive oil