- With the rack in the highest position, preheat the oven to 425°F (220°C).
- In a pot over medium heat, brown the pancetta and mushrooms in half of the oil until nicely browned, about 8 minutes. Add the leek and Swiss chard stems. Cook for 2 minutes. Season with salt and pepper.
- Pour in the broth and bring to a boil. Add the orzo. Simmer until the orzo is cooked, about 6 minutes. Add the Swiss chard leaves and mix well. Adjust the seasoning.
- Meanwhile, brush the bread with the remaining oil and sprinkle with the cheese. Place on a baking sheet. Bake for 5 minutes. Turn the oven to broil and continue to cook until the cheese is nicely browned. Sprinkle with the chives.
- Serve the soup in bowls with the cheese toast.