1. Remove stems from portobello mushrooms by twisting off or cutting flush with caps.
2. Using a spoon, gently scrape out dark gills from underside of caps while keeping mushroom structure intact.
3. In bowl, whisk together balsamic vinegar, olive oil, minced garlic, thyme, salt, and pepper until well combined.
4. Brush both sides of mushroom caps generously with marinade and let sit 15-20 minutes for flavor absorption.
5. Preheat grill to medium heat and ensure grates are clean and lightly oiled.
6. Place mushrooms on grill gill-side down and cook 4-5 minutes per side until tender with good grill marks.
7. During last minute of cooking, top each mushroom with Swiss cheese slice and allow to melt.
8. Toast burger buns on grill for 1-2 minutes until lightly golden.
9. Assemble burgers by placing cheese-topped mushroom on bun with lettuce, tomato, and desired toppings.
10. Serve immediately while mushrooms are hot and cheese is melted.

Nutrition Information (Per Burger):

• Calories: 285
• Carbohydrates: 28g
• Protein: 15g
• Fat: 14g
• Fiber: 5g
• Sodium: 520mg
• Selenium: 25% DV (from mushrooms)
• Calcium: 20% DV (from Swiss cheese)

High in protein and selenium, plus beneficial compounds from mushrooms with heart-healthy fats.

Notes:

• Remove dark gills to prevent bitter flavor and soggy texture
• Don’t skip marinating time—flavor penetration is crucial
• Grill over medium heat to cook through without burning
• Pat mushrooms dry after marinating but before grilling for better searing
• Serve immediately for best texture and temperature

Storage Tips:

• Marinate mushrooms up to 4 hours ahead for enhanced flavor
• Store grilled mushrooms refrigerated up to 3 days for salads
• Don’t assemble burgers ahead—mushrooms release moisture over time
• Leftover mushrooms excellent sliced cold in sandwiches

Serving Suggestions:

• BBQ party: Grill alongside meat options for inclusive entertaining
• Vegetarian feast: Serve with grilled vegetables and corn on the cob
• Casual dinner: Pair with sweet potato fries and coleslaw
• Healthy option: Use lettuce wraps instead of buns for low-carb version

Mix It Up (Recipe Variations):

• Mediterranean Style: Add sun-dried tomatoes, pesto, and goat cheese
• BBQ Version: Use barbecue sauce and cheddar with crispy onions
• Gourmet Upgrade: Serve on brioche with truffle aioli and arugula
• Mexican Twist: Add avocado, salsa, and pepper jack cheese

What Makes This Recipe Special:

These burgers demonstrate how vegetarian cooking can be genuinely satisfying when it celebrates ingredients for their natural qualities rather than trying to mimic meat. The combination of umami-rich mushrooms with tangy balsamic marinade creates depth and complexity that appeals to all palates, proving that plant-based meals can be the star of any cookout.