For the poached cod: Pat the cod dry with a paper towel, sprinkle it with salt and black pepper and let sit at room temperature for 5 minutes.
Heat a deep medium nonstick or enamel skillet over medium-high heat. Add the coriander seeds and pink peppercorns and cook until fragrant, about 1 minute. Slowly add the olive oil and bring the oil to 180 degrees F. Carefully add the cod to the oil. The cod should be fully submerged; if it's not, gently flip the fillets halfway through cooking, or add more oil to the skillet. Cook until the cod is opaque, 8 to 10 minutes.
Meanwhile, for the dressing: Combine the creme fraiche, buttermilk, vinegar, cilantro and peppercorns in a blender and puree. Add salt to taste.
For the avocado salad: Combine the avocado, radishes, shallot and teardrop peppers in a medium bowl. Sprinkle with a pinch of salt and a splash of champagne vinegar and toss gently; stir in the cilantro.
Using a fish spatula, transfer the cod to a paper towel-lined plate. Place 1 piece of cod in the center of each of serving plates. Tuck the avocado salad next to the cod. Drizzle the salad with dressing and top with the crushed fried onions.