Mushroom Sliders

Details

Ingredients

• 1 pound lean ground beef, or more to taste
• 1 large egg
• 1 small onion, finely chopped
• 1 cup finely chopped mushrooms
• 1 teaspoon ground black pepper
• ½ teaspoon garlic salt
• salt to taste
• 6 portobello mushrooms, or more to taste
• 1 green bell pepper, halved and seeded
• 1 red bell pepper, halved and seeded
• 1 yellow bell pepper, halved and seeded