Quick Polish Zapiekanka with Mushrooms and Cheese

Ingredients

• 1 demi-baguette or 1/2 French baguette, halved lengthwise
• 1 tablespoon unsalted butter
• 1 teaspoon olive oil
• 7 ounces white or cremini mushrooms, thinly sliced
• 1 small onion, finely chopped
• 1 clove garlic, minced
• Pinch of salt and black pepper
• 1 cup shredded mozzarella cheese
• 2 tablespoons ketchup
• 1 tablespoon chopped fresh chives or green onions
• 1 teaspoon dried oregano (optional)
• 2 tablespoons sliced pickles or pickled cucumbers
• 2 tablespoons sliced cooked ham or sausage (omit to keep vegetarian)