In a large bowl, combine mayonnaise, white balsamic vinegar, olive oil, Dijon mustard, finely minced garlic, oregano, salt, and pepper. Whisk these ingredients until smooth, then fold in sliced red onion, cucumbers, and olives. Gently mix to coat the vegetables, followed by adding the shredded iceberg lettuce. Let the grinder salad marinate while you toast the bread.

Preheat your oven to 425°F (220°C). While it heats, slice your crusty bread horizontally. Place slices on a baking sheet, layering each with sharp cheddar cheese and roasted turkey. Toast in the oven for about 5 to 10 minutes, watching closely until the cheese is perfectly melted and the bread is a delightful golden brown.

Once your bread is toasted to perfection, remove it from the oven and let it cool slightly. Next, carefully layer sliced avocado on one half of the bread, ensuring an even spread for a creamy texture. Generously pile on the prepared grinder salad on top of the avocado, allowing some ingredients to tumble over for a rustic look. Place the other half of the toasted bread atop to complete your Turkey Avocado Grinder Sandwich.

Slice the sandwich in half, exposing the vibrant layers, and serve right away to enjoy the medley of flavors and textures.