Preheat the oven to 375 degrees. Line a half sheet pan with heavy duty foil and lightly spray the foil.
Heat a large saute pan over medium heat. Add the 1 teaspoon of olive oil and swirl to coat the pan. Add the diced onion and sweat until the onions are just softened. Add the garlic and Italian seasoning and stir until fragrant.
Place the ground turkey into a large mixing bowl. Add the onion and garlic mixture, pinch of salt, black pepper, and bread crumbs. Mix well. and scoop out golf ball sized pieces onto the foil lined sheet pan. Once all of the balls are formed, place the pan into the preheated oven and bake for 10 minutes, or until the meat is no longer pink in the middle.
While the meatballs are cooking, return the saute pan to high heat and add the remaining 1 Tablespoon olive oil. Swirl the pan to coat and add the mushrooms. Saute the mushrooms until they are well browned and beginning to look a little dry. Add the onions and saute until they are nearly softened. Add the bell pepper and saute until hot. Add the tomato sauce and lower the heat to a gentle simmer. The meatballs should be done by now. Place the meatballs into the sauce and stir gently to coat.
While the meatballs are enjoying their tomato bath, split the baguette open using a serrated knife, making sure to leave one side attached, like a book. Place the baguette, split side down onto the sheet pan and place it in the oven to lightly toast. About 5 minutes.
Remove the bread from the oven and turn the cut side up. Line up the meatballs down the middle of the bread and top with the veggies and sauce. Sprinkle on the cheese and return to the oven for another 5 minutes to melt the cheese.