About this Recipe

Portobello mushrooms are naturally thick and meaty, making them a satisfying beef alternative for vegetarians, vegans (when cheese is omitted), or anyone looking to add more plant-based meals to their routine. The marinade — a simple blend of balsamic vinegar, low-sodium soy sauce, olive oil, chopped rosemary and a robust steak seasoning like Montreal — delivers bold, savory flavor and helps the caps develop a rich, grilled taste. This recipe is ideal for meatless Mondays or any night you want a flavorful, lower-calorie sandwich option.

Feel free to swap the Swiss cheese for mozzarella, feta, cheddar, or use roasted red pepper and fresh basil for a different flavor profile. Whole wheat buns and baby spinach keep the sandwich light and nutritious without sacrificing taste.

More Portobello Mushroom Recipes

• Veggie Lasagna Stuffed Portobello Mushrooms
• Philly Cheesesteak Stuffed Portobello Mushrooms
• Portobello Shepherd’s Pie

Recipe

Ingredients

• 4 portobello mushroom caps
• 2 tbsp balsamic vinegar
• 1 tbsp low-sodium soy sauce
• 1 tbsp olive oil
• 1 tbsp chopped rosemary
• 1½ tsp steak seasoning (such as Montreal)
• 4 thick slices red onion
• 4 oz reduced-fat Swiss cheese, sliced thin (or substitute)
• 4 thin slices tomato
• ½ avocado, sliced thin
• Baby spinach
• 4 whole wheat low calorie buns

Instructions

1. In a large bowl, whisk together the balsamic vinegar, soy sauce, olive oil, chopped rosemary, and Montreal steak seasoning until well combined.
2. Add the portobello caps to the bowl and spoon the marinade over them, turning each cap so it’s evenly coated. Let them stand at room temperature for 20–30 minutes, turning them a couple of times to marinate both sides.
3. Heat a grill or indoor grill pan over medium heat. Lightly oil the grate or spray the grill pan to prevent sticking.
4. Place the marinated mushrooms on the grill, reserving any leftover marinade for basting. Grill for about 5–7 minutes per side, basting frequently with the reserved marinade, until mushrooms are tender and nicely charred.
5. During the last minute of grilling, place the cheese on top of each mushroom so it can melt slightly.
6. While the mushrooms cook, grill the onion slices for about 1 minute per side until slightly softened and charred. Toast the buns on the grill until golden.
7. To assemble, layer baby spinach on the bottom bun, add the grilled portobello with melted cheese, then top with grilled onion, sliced tomato, and avocado. Close with the top bun and serve immediately.

Nutrition (per loaded burger)

Calories: 295 kcal • Carbohydrates: 31 g • Protein: 21 g • Fat: 13 g • Saturated Fat: 1 g • Sodium: 594 mg • Fiber: 11 g • Sugar: 6 g

Tips & Variations

• Vegan option: Omit the cheese or use a plant-based cheese alternative and choose vegan buns.
• Cheese alternatives: Try mozzarella for a milder flavor, cheddar for a sharper bite, or crumbled feta for a tangy finish.
• Herb swaps: If you don’t have rosemary, thyme or oregano make good substitutes and pair well with the balsamic marinade.
• Grill alternatives: If you don’t have a grill, use a stovetop grill pan or broil the mushrooms on high for a similar charred effect—watch closely to avoid burning.
• Make-ahead: Marinate the mushrooms in the refrigerator for up to 24 hours for deeper flavor. Bring them to room temperature before grilling for even cooking.
• Serving suggestions: Serve with a fresh side salad, roasted vegetables, or sweet potato fries for a complete meal.

Final Notes

These grilled portobello burgers balance bold savory flavors with fresh toppings, delivering a satisfying texture and taste that appeals to both vegetarians and meat eaters. The simple marinade is the key to infusing the mushrooms with a meaty, umami-rich flavor while keeping the recipe quick and approachable. Experiment with different cheeses, toppings, or bun types to make this sandwich your own.