3 tablespoons extra-virgin olive oil, plus more for drizzling
1 can black beans, rinsed and drained
2 cups packed coriander leaves, plus more for serving
3/4 cup sour cream
1 tablespoon fresh lime juice, plus wedges for serving
1/4 teaspoon plus a pinch chilli powder
4 cups shredded red cabbage (from 1/2 head)
1 tuna steak (1 inch thick), chilled, cut along the grain into thirds
Flaky sea salt and sliced radishes, for serving
In a small saucepan, combine rice and 1 1/2 cups water. Season with kosher salt and pepper; drizzle with oil. Bring to a boil, then reduce heat to low; cook, covered, until water is absorbed, 12 to 15 minutes.
Remove from heat; let stand, covered, 10 minutes. Stir in beans. In a food processor, puree cilantro, sour cream, lime juice, 2 tablespoons oil, and pinch of chilli powder. Season with kosher salt. Toss cabbage with 1/4 cup dressing; season with kosher salt and pepper.
Heat a small skillet over high. Pat tuna dry; season with salt and remaining chilli powder. Swirl remaining oil in skillet; add tuna.
Cook until golden brown on all sides, 1 to 2 minutes total. Let stand 5 minutes; slice thinly against the grain. Sprinkle with flaky salt.
Serve with rice mixture, slaw, radishes, cilantro, lime wedges, and dressing.