Grilled Portobello Swiss Burger - Weber Seasonings

Ingredients

• <strong>Mushroom Marinade</strong>
• ⅓ cup olive oil
• 1½ tsp balsamic vinegar
• 1 tbsp Dijon mustard
• 1½ tbsp <a href="/products/flavor-bomb-burger-seasoning/" target="_blank" rel="noopener">Weber® Flavor Bomb Burger Seasoning</a>
• 4 portobello mushroom caps
• <strong>Burgers</strong>
• 4 slices Swiss cheese
• 4 brioche burger buns, toasted
• 4 leaves butter lettuce
• 4 slices tomato
• 4 slices red onion
• 4 tbsp mayonnaise