In a pot, heat the butter until melted. Turn off the heat and add the salt, chili powder, paprika, pepper, onion powder, granulated garlic, dried thyme, oregano and cayenne and allow the spices to bloom. (Alternatively, combine all the spices and the butter in a microwave-safe bowl. Cover with a wet paper towel and microwave on high for 45 seconds. Whisk together and let cool completely.)
Heat a grill to medium high and cover.
Coat both sides of the fish with the blackening spice/butter mixture.
Clean the grill grates very well and coat with vegetable oil and nonstick spray for that super nonstick double coverage.
Grill the fish on high, uncovered, until the internal temperature registers 130 to 135 degrees F, 3 to 4 minutes a side. Do not move the fish prematurely or it will stick. Only use a thin, metal fish spatula to flip.
Put a piece of fish on each bottom bun and top with Pickled Escovitch Peppers and shredded lettuce. Add a schmear of Mango Aioli on the top buns, close and eat!
Pickled Escovitch Peppers:
Combine the vinegar, sugar, honey, thyme, tarragon and some salt in a small saucepan and bring to a boil. Turn off the heat and add the peppers and onion. Let cool to room temperature.
Mix together the mayonnaise, mango chutney and lime zest and juice in a bowl. Season with salt and pepper.