Meanwhile, heat the oil in a large saucepan over medium-high heat. Add the onion, bell pepper, garlic, 1 teaspoon salt, and 1/4 teaspoon black pepper. Cook, stirring occasionally, until softened, 5 to 7 minutes.
Stir in the cumin and cook 1 minute.
Add beans, oregano, and 1 cup of water. Simmer, covered, for 10 minutes.
Add the vinegar and smash some of the beans with the back of a fork to thicken.
Serve the beans over rice and top with the radishes and cilantro.