To make the rice: In a small or medium pot, stir together the 1 ¾ cups water 1 cup basmati rice, 1 tablespoon olive oil, and ½ teaspoon kosher salt. Bring to a boil. Stir once, cover, and simmer on low for 10 minutes, or until there is no more water around the rice if you tilt the pot. Turn off the heat and keep the cover on for another 5-10 minutes. Fluff with a fork, stir in the 2 tablespoons chopped fresh cilantro and juice and zest from ½ lime, and adjust seasonings if necessary.
While the rice is cooking, make the beans. Sauté the diced 1 small onion in the 1 tablespoon olive oil over medium-high heat, in a medium pot, until softened and beginning to brown (about 2-3 minutes).
Add the 1 teaspoon cumin and ½ teaspoon kosher salt and stir to coat. Add the drained and rinsed 28 oz. canned black beans and 1 cup water. Stir, bring to a boil, and simmer uncovered for about 10 minutes.
Turn off the heat. Use a potato masher to mash the beans a few times, thickening the mixture, but leaving most of the beans intact. If you don't have a potato masher, you can use a fork on the side of the pot, or a few brief pulses with an immersion blender.
Stir in the juice and zest from the remaining ½ lime and 2 tablespoons chopped fresh cilantro. Taste and season with more salt if necessary.
Serve the beans on top of the rice as a side or meal. Top with fixings such as shredded cheese, pico de gallo, diced avocado, hot sauce, etc., if you want.