In a small bowl, emulsify the olive oil, honey, apple cider vinegar, red pepper flakes, salt, and pepper using a whisk.

Preheat a cast-iron grill pan to 200 degrees Celsius (medium-high heat).

Remove excess moisture from Halloumi slices using paper towels to ensure optimal Maillard reaction.

Place Halloumi on the grill and sear for 120 seconds per side until distinct char marks form and the core softens.

In a large chilled bowl, toss the arugula, watermelon, and red onion with 50% of the prepared dressing.

Transfer the mixture to a serving platter and arrange the warm grilled Halloumi across the surface.

Drizzle the remaining dressing specifically over the cheese and garnish immediately with the torn mint leaves.