Heat the oil in a large heavy-bottomed pot or caldero over medium heat.
Add the diced bacon or tocino and cook until it turns golden and crispy.
Add the diced onion, green bell pepper, and aji dulce (if using). Sauté for about 5 minutes, or until the vegetables soften and become fragrant.
Stir in the minced garlic and cook for 30–60 seconds until fragrant.
Add the cumin, oregano, salt, and black pepper, stirring to coat the vegetables in the spices.
Add the rinsed white rice to the pot and stir until each grain is coated in the sofrito mixture.
Toast the rice for about 1–2 minutes to absorb the flavors.
Stir in the cooked black beans, then pour in the reserved bean cooking liquid (about 3 cups total). If you don’t have enough bean liquid, add water until you reach 3 cups. Mix gently to combine.
Bring the mixture to a boil over medium-high heat. Taste for seasonings here, and adjust with salt or even more cumin, if desired.
Once it starts boiling, reduce the heat to low, cover tightly, and cook for 20–25 minutes, or until the rice is tender and the liquid is absorbed. DO NOT OPEN BEFORE 20-25 MINUTES!
Turn off the heat and fluff the rice gently with a fork.
Drizzle the white vinegar over the black beans and rice, then cover again and let it rest for 5–10 minutes.
