Mushroom Cheeseburgers

Ingredients (9)

• 1/4 cup chopped canned mushrooms
• 1/4 cup finely chopped onion
• 1 teaspoon dried oregano
• 1/2 teaspoon salt
• 1/2 teaspoon pepper
• 1 pound ground beef
• 4 slices process American cheese
• 4 hamburger buns, split
• Lettuce leaves, optional