Place a rack in middle of oven; preheat to 375°. Pat 2 lb. skinless, boneless chicken thighs (6–8) dry with paper towels and sprinkle all over with 1 tsp. freshly ground pepper, 1 tsp. ground cumin, and 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt. Set aside.

Set aside a small handful of 1 bunch cilantro, rinsed well, tough stems removed, for serving if desired. Blend 1 medium onion, chopped, 1 medium green bell pepper, ribs and seeds removed, chopped, 6 garlic cloves, and remaining cilantro in a blender on high speed until mostly smooth. Set aside.

Heat 3 Tbsp. extra-virgin olive oil in a large high-sided ovenproof skillet with a lid over medium-high. Working in batches if needed, cook reserved chicken in a single layer, undisturbed, until deeply browned underneath, 6–8 minutes. Transfer to a plate, arranging browned side up. (Chicken will still be raw.)

Cook reserved purée in same pan over medium heat, stirring often, until it dries out into a loose, tomato-paste-like texture, 6–8 minutes. Add one 15.5-oz. can black beans, rinsed, 1½ cups long-grain white rice (do not rinse), remaining 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, and 1½ cups water; bring to a simmer, then immediately remove pan from heat.

Arrange chicken, browned side up, on top of beans and rice; cover pan. (If lid doesn’t fit well, cover pan with foil first.) Transfer to oven; bake 45 minutes. (Be exact; don’t peek.) Turn off oven; let sit in oven (still covered) 10 minutes.

Remove pan from oven, uncover, and fluff rice with a fork. Scatter crumbled Cotija cheese (if using) and cilantro if you reserved some over. Serve with lime wedges if desired.