Place the peppers in the bowl of a food processor and season with salt and pepper. Add the lemon juice and hot sauce (eyeball it), then put the lid in place and turn on the processor. Add the EVOO in a thin stream (eyeball it as well) and process until smooth.
Pre-heat the broiler. Using your fingers, check the crabmeat for pieces of shell. In a medium size bowl, combine the crab and seafood seasoning. Add the celery, tarragon and scallions to the crab and toss with the red pepper dressing; adjust the seasoning, to taste.
Toast the English muffins under the hot broiler, then lightly butter them. Top each with a small handful of watercress, then with a scoop of the crab salad. Pat down the salad a bit, then top with a handful of cheese and return to the broiler to melt the cheese, about 1-2 minutes. Remove and serve immediately.