How to Make It
Preheat the oven to 400°. On a rimmed baking sheet, toss the ciabatta cubes with 1 tablespoon of the olive oil and bake, tossing occasionally, until crisp and golden, 8 to 10 minutes. In a large bowl, whisk the vinegar with the garlic and let stand for 10 minutes.
Roast the red and yellow peppers directly over a gas flame or under the broiler, turning, until charred all over. Transfer the peppers to a bowl, cover tightly with plastic wrap and let cool, about 15 minutes. Peel, stem and seed the peppers, then cut them into 1 1/2-inch pieces. Add to the vinegar in the bowl.
Light a grill or preheat a grill pan and oil the grate. Season the onion and corn with salt and pepper and grill over high heat, turning as necessary, until tender and nicely charred, about 6 minutes. Cut the kernels off the cob. Add the corn, onion, croutons, fennel, tomatoes, crabmeat and 1/4 cup of the olive oil to the bowl and toss well. Season with salt and pepper.
In a large nonstick skillet, heat the remaining 2 tablespoons of olive oil until shimmering. Season the fish with salt and pepper and add to the skillet skin side down. Cook over moderately high heat, gently pressing with a spatula, until the skin is browned and crisp, 3 to 4 minutes. Flip the fillets and cook until the fish is white throughout, 2 to 3 minutes longer.
Toss three-quarters each of the parsley and mint leaves with the panzanella and mound on plates or a platter. Top with the fish, garnish with the remaining parsley and mint and serve immediately.