Preheat the oven to 375 degrees.
Clean the mushrooms with a damp paper towel and remove the stems from the inside. Chop up the stems and save for the filling.
6 portobello mushrooms
Place the cleaned mushrooms on a sheet pan greased lightly with cooking spray or a drizzle of olive oil.
6 portobello mushrooms
Heat 1 ½ tbsp. of olive oil in a saute pan over medium heat and add the onion, mushroom stems, zucchini, bell pepper and garlic, along with the dried herbs and salt and pepper. Saute until soft, about 5 minutes.
Add in the spinach until it is wilted, about 2 minutes.
2½ cups spinach
Let the filling cool slightly. Spoon filling into mushroom caps.
Bake in the preheated oven for 7 minutes.
Meanwhile, make the topping by combining the parmesan cheese, crushed Garlic OMG! Pretzels, and remaining olive oil in a small bowl.
1 cup Garlic OMG! Pretzels
Remove mushroom caps from the oven and add the topping; return to the oven and bake for 5 more minutes until the topping is warm.
Serve with a side salad and enjoy!