Chilled Beet and Watermelon Soup

Ingredients

• 1 tbsp vegetable oil
• 1 medium onion, peeled and sliced
• 1/2 pound beets, peeled and roughly diced
• 4 cups chicken stock or low-sodium chicken broth
• 1 tsp salt
• 2-1/2 cups diced seeded watermelon (rind removed)