Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper. Preheat a grill pan over medium heat.
Put the salmon fillets on the prepared baking sheet, season with salt and pepper and brush with the barbecue sauce. Bake until firm and the thickest part flakes through, 12 to 15 minutes. Let rest for 5 minutes, then flake with a fork.
Meanwhile, brush the corn with the olive oil and season with salt. Put on the grill pan and grill, turning every 2 minutes, until grill-marked and tender on all sides, about 8 minutes total. Let cool, then slice the kernels off the cob.
Add the watercress and romaine to a large serving bowl. Top with the salmon flakes, corn, tomatoes, croutons, bacon, egg and avocado. Pour on about 1/3 cup of the Ranch Dressing, toss and serve.
Add the mayonnaise, yogurt, buttermilk, chives, parsley, garlic powder, salt and pepper to a medium bowl and mix to combine. Refrigerate until ready to serve.