Place the poblano pepper under a broiler or over a gas flame, turning occasionally until the skin is charred and blistered.
Transfer the pepper to a bowl and cover for 5 minutes, then peel away the skin, remove the seeds, and finely dice.
In a small bowl, combine the diced poblano, finely diced red onion, minced garlic, lime juice, and chopped cilantro to create the salsa.
Pat the cod fillets dry with a paper towel and season both sides evenly with sea salt, black pepper, and ground cumin.
Heat the avocado oil in a large non-stick skillet over medium-high heat until the oil is shimmering.
Carefully place the cod in the skillet and sear for 3 to 4 minutes per side until the fish is opaque and flakes easily with a fork.
While the fish cooks, gently warm the black beans in a small saucepan over low heat until heated through.
Plate the cod over the warm black beans and spoon the smoky poblano salsa generously over the top before serving.