Heat large skillet over medium heat. Add bacon and cook 3 to 4 minutes per side, until browned and crisp. Transfer bacon to paper towel–lined plate, leaving fat in skillet, and set aside.
Return pan with fat to medium heat, add shallot and garlic and cook about 2 minutes, until fragrant, tender, and just beginning to brown. Scrape garlic and shallot into medium heatproof bowl, along with fat. Don’t wash pan; just set aside.
To prepare vinaigrette: Add vinegar, honey, mustard, ½ teaspoon salt, and pepper to taste to bowl with garlic and shallot. Whisk or mix with fork until well emulsified. Add avocados and mangoes, gently toss together, and set aside.
Heat oil and butter over high heat in skillet used for bacon until oil is hot but not smoking and butter has begun to foam. Add shrimp without crowding pan. (Cook them in two batches if necessary). Season with ½ teaspoon salt and pepper to taste, and cook, flipping over once, until seared and browned, no more than 2 minutes. Transfer to bowl.
Open buns or rolls, trying not to separate tops from bottoms, and arrange layer of cooked shrimp on bottom of each. Top shrimp with avocado and mango mix and crown each with couple slices bacon. Close sandwiches and serve.