Grilled Portobellas Stuffed with Sausage, Spinach, and Mozzarella

3/4 lb. turkey sausage
1 med. yellow onion, sliced
1/2 c. dry red wine
8 oz. fresh spinach leaves, stems removed and coarsely chopped
1/2 c. water
Salt and pepper
4 tbsp. chopped fresh basil leaves
3 tbsp. chopped fresh flat-leaf parsley
8 oz. fresh mozzarella, diced
6 to 8 lg. portobello mushrooms, stems removed
Olive oil, for brushing
1-2 tomatoes, thinly sliced

Preheat grill to medium-high heat. Oil grates.

In a skillet over medium-high heat, brown sausage and break into small pieces. Add sliced onion and cook until tender and translucent, about 5 to 7 minutes. Add wine and cook until wine is completely reduced. Add spinach and water to pan, and season with salt and pepper. Cook until spinach has wilted, about 2 minutes. Remove from heat and stir in 2 tbsp. basil, 2 tbsp. parsley, and cheese. Stir together and allow to cool slightly.

Brush mushroom caps on both sides with olive oil and season with salt and pepper. Place on grill, cap side down, and cook until golden brown, about 4 minutes. Remove mushrooms from grill and place on a flat surface, cap side down. Fill mushrooms with sausage mixture and top each with one or two slices of tomato. Return to grill, cap side down, and close cover. Cook until mushroom and filling have heated through, cheese is melted, and tomato is soft, about 5 minutes. Remove to a serving platter and sprinkle with the remaining basil and parsley.