In a medium saucepan prepared with cooking spray, saute onion, tomato, and garlic at medium heat stirring often (about 2-3 minutes).
Add broth, salsa, and cumin. Stir to combine. Bring to a boil. Add spinach (if desired).
Meanwhile, cook your carnitas per package instructions.
Remove carnitas from the microwave and with a spatula, scrape the contents into the saucepan, stirring to combine flavors. Boil for 2 minutes and remove from heat.
Move soup to a large bowl, and garnish as desired.