Portobello Mushroom Burger with Avocado Chimichurri

large portobello mushrooms

red bell pepper, sliced into ¼ inch rings

red onion, peeled and sliced into ¼ inch rings

large handful of fresh spinach

Extra virgin olive oil

dried oregano

kosher salt and freshly ground black pepper

avocado, peeled and pitted

garlic, peeled

olive oil

flat leaf parsley leaves

cilantro leaves

juice of 1 lemon

red wine vinegar

red chili flakes

pieces flatbread pitas or 2 soft burger buns

Smoked mozzarella cheese, optional