Combine the bulgur and boiling vegetable broth in a medium bowl; cover and let sit until tender, about 20 minutes. If you used water, stir in 1/2 tsp. of salt to mixture. If needed, drain the bulgur in a fine mesh sieve; set aside.

Preheat oven to 400 degrees. Line a 9x13 pan with foil and place the peppers (cut side up) in the pan; set aside.

Heat 2 Tbsp. oil in a large skillet over medium heat. Saute the onions until softened, about 5 to 7 minutes. Add the mushrooms and cook for 2 to 3 minutes. Next, add garlic and cook for an additional minute. Stir in spinach and 1 Tbsp. of water and cook (covered) until wilted, about 3 to 5 minutes. Remove from heat and stir in parmesan cheese and salt and pepper to taste.

Mix the bulgur and spinach mixture together and spoon mixture into the peppers. Pour 4 Tbsp. of water into the bottom of the pan, cover with foil or lid and bake until the peppers are tender, 30 to 45 minutes, depending on how soft you want the peppers.

Coat a small skillet with non-stick spray and heat over medium heat. Add the pine nuts and cook until golden brown, about 1 to 2 minutes, stirring constantly.

Sprinkle the toasted nuts on top of the stuffed peppers and serve.