Preheat the oven to 350 degrees F.
For the Vegetables - In a medium size bowl, add the onions, zucchini, garlic, and Serrano pepper. Set aside.
For the Mushrooms - Remove the stems from the mushrooms. If the mushrooms are nice and fresh the stems should just snap off.
Dice the stems and add them to the bowl with the vegetables.
Sautéing the Vegetables - Heat a medium size skillet on medium heat, and add olive oil and the vegetables from the bowl.
To the pan, add salt, pepper, and oregano. Stir together and sauté while stirring occasionally for 7 minutes.
To the pan, add the chopped kale and stir. Sauté until the kale starts to turn a darker color (about 3 or 4 minutes).
Preparing the Filling - Transfer the vegetables from the pan back into the bowl they were in.
To the bowl, add bacon bits (dice the bacon if necessary), tomatoes, mozzarella and panko bread crumbs. Stir together.
Stuffing the Mushrooms - Gently stuff the mushrooms with the filling so that the stuffing is in the shape of a mound on top of the mushrooms. There should be enough stuffing to “overstuff” each mushroom.
Place each stuffed mushroom on an ungreased cookie sheet.
Bake uncovered in a preheated oven until the cheese melts (about 10 to 15 minutes).