While waiting for grill to heat to medium, rinse and dry the Portobello caps.
Layer 2 tbsp of marinara sauce on each mushroom, with the bottom facing up.
Add two slices cheese to each cap. Once the grill is heated up, grill sausage until charmarks form on both sides. Meanwhile, put the mushrooms on a large double layer piece of foil.
Place the mushroom pizzas/foil on the grill and heat until the cheese is fully melted and sauce begins to bubble (about 6-8 minutes).
Remove the mushrooms and sausage. Slice the sausage and layer on top of the pizzas.
Sprinkle the chopped sun dried tomatoes, spinach and basil on the pizzas.
Pair with an arugula salad for a perfect light personal pizza!