Thinly slice the onions (it's helpful to use a mandolin).  Place onions in a large container. 

Heat the vinegar, water, sugar, and salt in a medium saucepan over medium heat. Stir until the sugar and salt dissolve, about 1 minute and pour over the onions. Set aside to cool to room temperature.

Pickled red onions will be ready to eat once they're bright pink and tender - about 1 hour, store any leftover onions in the fridge.

Cooking Instructions:

Preheat oven to 350° F. Place frozen meatballs on baking sheet and cook 20-25 minutes, set aside. 

Bring a large pot of water to a boil, cook vermicelli noodles according to package directions. Toss cooked noodles in stir fry sauce. Set it aside. 

In a large pan set over medium heat add 2 tablespoons of olive oil, and the sliced shitake mushrooms, cook stirring occasionally for 8-10 minutes until mushrooms are caramelized and tender. Remove the mushrooms and set aside. 

In the same pan add 1 tablespoon of olive oil and baby spinach season with salt and black pepper cook until the spinach is just wilted 2-3 minutes. Remove the spinach and set aside.