Best Portobello Steaks

Name: Best Portobello Steaks
Ingredients: 4 large portobello mushrooms (stems removed, wiped clean); 2 tbsp balsamic vinegar; 2 1/2 tbsp extra virgin olive oil; 2 tbsp low sodium soy sauce (gluten-free if needed); 3 garlic cloves (minced); 1 tsp onion powder; 1 tsp paprika; 1/3 tsp cumin; 1/3 tsp smoked paprika; Black pepper to taste; Cayenne pepper (optional)