Preheat a grill pan or outdoor grill to medium-high. Place the peach halves cut-side down and grill for 2–3 minutes until clear grill marks form and the flesh is lightly caramelized. Flip and grill for 1–2 minutes more. Remove and let cool slightly. Peaches should be lightly charred in spots, never burned.
Heat the water to 90–95°C (195–203°F). Add the black tea bags and steep for 2½–3 minutes maximum. Remove the tea bags without squeezing and let the tea cool to lukewarm.
Roughly chop the grilled peaches. In a small saucepan, combine the peaches, sugar, and water. Bring to a gentle simmer over medium-low heat and cook for 8–10 minutes, just until the peaches soften and release their caramelized aroma. Do not reduce or thicken.
Remove the syrup from heat and add the lemon zest strip. Let steep for 3 minutes only, then remove and discard the zest. This is aroma, not flavor.
Strain through a fine-mesh sieve into a bowl or measuring jug. Do not press the pulp. Discard solids and let the syrup cool completely.
Stir 120–160 ml of the cooled grilled peach syrup into the tea. Taste and adjust carefully — peach should be present but clean, never jammy.
Refrigerate for 1–2 hours until fully cold and integrated.
Fill glasses with ice, pour over the chilled grilled peach iced black tea, and garnish with grilled peach slices.
