1. Preheat the grill.
2. Mix the olive oil, garlic, salt, pepper and 1/2 teaspoon of the basil together. Remove the stem from the mushroom and brush both sides of the cap with the olive oil mixture. Set aside.
3. Mix the cheese, the remaining 1/2 teaspoon of basil, salt and pepper together. Set aside.
4. Grill the mushroom until they are soft in the center, about 3 to 4 minutes on each side. Slice each cap on the diagonal into 1" strips.
5. Spread 2 halves of bread with the cheese mixture, then top with the spinach or arugula, a slice of roasted red pepper and the sliced Portobello. Place the other half of the bread on top.
Serving Size: 1 sandwich