In a large skillet, heat olive oil over medium heat. Add onion and garlic, and sauté for 3 minutes.
Add mushrooms, soy sauce, and balsamic vinegar, and sauté for 2 minutes.
Add ground turkey. Cook over medium heat until no longer pink, about 7 minutes, using a spatula to break apart. Stir in Italian seasoning.
Add pizza sauce and black pepper, and mix over low heat for 3 minutes.
Preheat often to 400°F.
Separate whole English muffins into 16 halves, place on a baking sheet, and toast for 2 minutes.
Top each muffin half with about 3 tablespoons of the pizza sauce mixture and 1 tablespoon shredded cheese.
Place in the oven, and cook for 5 minutes, until cheese melts.