Bean-and-Fish Tacos

INGREDIENTS

• 1 Vidalia onion, thinly sliced into rings
• 2 limes, 1 juiced and 1 cut into wedges
• Coarse salt
• 1/3 cup finely chopped scallions (about 6)
• 3 tablespoons finely chopped jalapeno chiles (about 2)
• 3/4 cup finely chopped fresh cilantro, plus sprigs for serving
• 2 tablespoons plus 2 teaspoons extra-virgin olive oil, divided
• 3/4 pound meaty fish fillets, such as mahimahi
• 2 cups cooked beans, plus 1/4 cup cooking liquid
• 8 to 12 corn tortillas, toasted briefly over an open flame and wrapped in a cloth, for serving
• 4 ounces cotija or ricotta salata cheese, crumbled (3/4 cup), for serving
• 4 radishes, thinly sliced, for serving
• 1 head romaine lettuce, trimmed and shredded (2 cups), for serving