1 Tbsp olive oil
1 small onion, chopped
4 small red potatoes, cut into 1/2-inch pieces
1 pound button mushrooms, trimmed and quartered
1/4 tsp dried thyme
salt to taste
1 Tbsp tomato paste
2 cups water
10 ounces spinach
1 can nay beans, drained and rinsed
1 Tbsp red-wine vinegar, optional
In a large nonstick skillet or heavy pan, heat oil over medium heat. Add onion and potatoes; cook until onion is lightly crowned, 8 to 10 minutes. Add mushrooms, thyme, and salt; cook, stirring often, until mushrooms are tender, 8 to 10 minutes.
Stir in tomato paste, and 2 cups water; cover, and cook until potatoes are tender, 8 to 10 minutes.
Add half the spinach; cover, and cook until wilted, about 1 minute. Add remaining spinach and beans; cook (covered) until heated through. Stir in 1 tablespoon red-wine vinegar if desired. Season with salt and pepper, and toss to combine.