Slice the halloumi into thick pieces and pat dry with paper towels to help it crisp properly during cooking.
Heat olive oil in a skillet over medium heat. Cook halloumi for 2–3 minutes per side until deeply golden and crispy around the edges.
Lightly toast the bread until crisp and warm. This helps prevent the sandwich from becoming soggy.
In a small bowl, mix Bulgarian yogurt, garlic, lemon juice, and salt until smooth.
Spread lutenitsa generously over the toasted bread. Layer with crispy halloumi, tomatoes, cucumbers, greens, herbs, and yogurt sauce if using.
Finish with cracked black pepper and serve immediately while the halloumi is still warm and crispy.