Start by rinsing the tomatoes, I usually de-stem them as well. Roast the tomatoes in the oven (400F) for a half hour or so.
As the tomatoes roast, roughly chop 1/2 onion and peel 2 garlic cloves. Cook the onion and garlic in a glug of oil over medium heat in your soup pot. I usually leave the garlic cloves whole as all of this will be blended eventually.
When the onion is starting to brown add the onion-garlic mixture to a blender along with the roasted tomatoes and a single chipotle in adobo (or 1/2 chipotle for a milder version). Combine well and add this mixture back to the soup pot, cooking over medium heat for a couple minutes.
Add the remaining ingredients: 3 cups stock, 1/3 cup uncooked white rice, 1 can beans (drained and rinsed), 2 teaspoons Mexican oregano, pinch of cumin, 1/2 teaspoon salt, freshly cracked black pepper. Combine well and bring this mixture up to a boil. Reduce heat to a simmer (low on my stove), cover, and let cook for 15 minutes or until the rice is fully cooked. Note: try to keep a close eye on it starting around the 15 minute mark because the rice will continue to absorb the stock if left unattended.
Take a final taste for seasoning. I added pinches of salt and Mexican oregano at this point. Note: I used approx. 1 teaspoon of salt for this entire batch, but if using store-bought stock you may not need to use as much as I did.
Serve immediately and top with your choice of garnish. A squeeze of lime is really all you need, but I also topped with some Queso Fresco and freshly chopped cilantro.
This soup does not store well! The rice will continue to absorb liquid if stored overnight, so I tend to make it in smaller batches and eat all of it :) If you want to make a bigger batch for storage consider leaving out the rice until you're ready to serve, then simply reheat, add the rice, and cook for 15 minutes or until the rice is fully cooked.