Heat oven to 450F. Line a baking sheet with foil. Place mushrooms open end down. Brush caps with 1 tablespoon oil, vinegar, maple salt and pepper. Bake until tender, about 8 minutes. Drain excess juice off.
In a skillet over medium heat, heat 1 tablespoon oil. Add onion and cook until translucent, about 4 minutes. Add garlic, thyme, rosemary, beans and broth; season with pepper. Add spinach; cook until spinach is wilted (about 4 minutes).
Remove from heat and stir in prosciutto and parsley. Stuff the mixture evenly into the caps. Top each with panko and Parmesan.
Coat caps with cooking spray; bake until panko is golden, 10 minutes. Serve warm.