Wipe the top of the mushrooms with a damp paper towel to lightly clean. Remove the stem and scoop out all of the gills and discard. Place the portobellos top-down on a baking sheet and bake for 20 minutes.
While those are baking, add the garlic, shallots, and sun-dried tomatoes (and a bit of oil from the jar) to a medium frying pan. Sauté on medium heat for about 5 minutes, stirring frequently.
Add the beans, spinach, salt, Italian seasoning, pepper, and half of the parsley. Reduce heat to low and cook for 10 minutes, stirring occasionally.
When the mushrooms are done, remove them from the oven and stuff each one with the filling. Top with the remaining parsley and serve.