Gently clean portobello mushroom caps with cloth just prior to preparation.

In medium to large bowl, combine balsamic vinegar and olive oil, and whisk together with fork. Add mushroom caps to bowl and soak until mushrooms are saturated with marinade.

Remove mushroom caps from bowl and place on plate. Sprinkle with freshly ground black pepper and smoked paprika.

Gently coat grill, grill pan or large skillet with olive oil or nonstick spray and heat over medium heat.

Sear mushrooms for about 2 minutes on each side, until cooked through and mushroom caps darken in color. Set cooked mushrooms aside.

To assemble sandwich: coat bottom piece of baguette with spread. Add roasted bell pepper, arugula and cooked mushrooms.

In clean skillet over medium heat, sear assembled sandwich about 3 minutes on each side until bread is heated through.