Preheat the oven to 425°F.
Arrange the bacon on one side of a large sheet pan. Toss the halloumi with the olive oil and black pepper and spread it onto the other side of the pan.
Roast for 15–18 minutes, flipping the halloumi halfway through, until the halloumi is golden brown and the bacon is crisp.
Transfer the bacon to a paper towel-lined plate. Once cool enough to handle, roughly chop.
Allow the halloumi to cool for 5–10 minutes so it firms up slightly.
Meanwhile, whisk together the mayonnaise, red wine vinegar, garlic, salt, and pepper. Add water a little at a time until the dressing is smooth and drizzleable. Taste and adjust the vinegar if desired.
In a large bowl, combine the romaine, cucumbers, cherry tomatoes, avocado, red onion, dill, basil, chopped bacon, and roasted halloumi.
Drizzle generously with the dressing and toss until evenly coated.
Finish with plenty of fresh cracked black pepper and serve immediately.