Preheat the grill to medium-high heat. Alternatively, preheat the oven to 450 degrees F.
Remove the cardboard and plastic covering from the potato package. Add the onion pieces, 2 tablespoon of olive and the seasoning packet. Stir to coat.
Place the foil package directly on the grill (or in the oven) and cook for 20 to 25 minutes, stirring once halfway through.
In a medium bowl, stir together the mushrooms, 2 teaspoons of olive oil, rosemary and salt. Stir the mushrooms into the potato and onion mixture. Cook until the potatoes are tender when pierced with a fork, about 12 to 15 minutes, stirring halfway through.
Garnish with parsley. Serve.
Notes
Please note that I am not a medical or nutritional professional. I provide nutritional information for my recipes as a courtesy to my readers. It is calculated using the LoseIt! calculator. While I attempt to provide information that is as accurate as possible, you should calculate the nutritional information independently before relying on it.