Creamy Spinach and Zucchini Soup

1 large onion, chopped

6 cups water, divided

3 potatoes, chopped

3 zucchini, sliced

1 tablespoon low-sodium soy sauce

2 cups tightly packed spinach leaves

ground black pepper to taste

⅓ cup sliced fresh enoki mushrooms

Combine onion and 1/2 cup water in a large saucepan over medium-high heat; cook and stir until onion softens, about 3 minutes.

Pour remaining water into saucepan; add potatoes, zucchini, and soy sauce. Bring the water to a boil, reduce heat to low, place a cover on the saucepan, and cook for 35 minutes.

Stir spinach into the soup; season with black pepper. Continue cooking another 2 minutes; remove saucepan from heat.

Blend soup in batches in a blender until completely pureed. Return pureed soup to saucepan and place over medium-low heat.

Stir mushrooms into pureed soup; cook until the mushrooms are warmed through, about 5 minutes.