In a large bowl, add in the mayo, white balsamic vinegar, olive oil, mustard, garlic, oregano, salt, and pepper and mix until fully combined. Taste and adjust seasonings if needed.
Then add in the sliced red onion, sliced cucumbers, and sliced black olives and toss to coat in the dressing.
Shred the iceberg lettuce and then add to the bowl and gently toss until completely coated in the dressing. Set aside and let marinate while you make the sandwiches.
While the grinder salad marinates, preheat the oven to 425°F.
Slice your bread in half and layer with cheese and sliced turkey. Toast for 5-10 minutes until the cheese is melted and the bread is toasted.
Top with sliced avocado and a big pile of grinder salad for each sandwich.
Serve immediately! The dressing from the salad will make the bread soggy if it sits too long.
This recipe makes enough salad for 2 large sandwiches or 4 small ones so you might have a little grinder salad leftover. But it's delicious on its own or scooped up with potato chips!It's also pretty easy to scale up this recipe for a party or picnic! Make the salad up to a few hours in advance and assemble the sandwiches immediately before serving.