Fire up your grill and get it running hot - you want 450-500°F in your direct heat zone. Clean the grates thoroughly and oil them well to prevent sticking. While the grill preheats, pat the halloumi slabs completely dry with paper towels - any surface moisture will prevent proper searing and create steam instead of the bark we are after.

Prepare your vegetables by brushing all pieces with olive oil and seasoning with minced garlic, oregano, salt, and pepper. The oil coating is critical for preventing sticking and helps conduct heat for even cooking. Do not oil the halloumi - it has enough natural fat content and additional oil will cause flare-ups.

Start with the vegetables since they take longer than the cheese. Place the eggplant and onion wedges over direct heat first - they need 4-5 minutes per side. Add the bell pepper strips after 2 minutes, and the zucchini planks last since they cook fastest. You want good grill marks and slight char on all vegetables.

Once vegetables are nearly done, place the halloumi slabs directly over the hottest part of your grill. This is where timing becomes critical - halloumi needs exactly 2-3 minutes per side. You will hear it sizzle immediately and see the edges start to bubble. Resist the urge to move it around - let it develop that golden bark.

Flip the halloumi when you see golden-brown grill marks and the edges have firmed up. The second side cooks slightly faster, usually 2 minutes max. The internal temperature should reach about 140°F - hot enough to be creamy but not so hot that it melts through the grates. Remove immediately and let rest for 2 minutes.

Arrange the grilled vegetables on a serving platter and top with the halloumi slabs. Drizzle with fresh lemon juice and garnish with chopped parsley. Serve immediately while the cheese is still warm and has that perfect contrast between crispy exterior and creamy center.