How to Make It
In a saucepan of boiling salted water, blanch the basil until just wilted. Drain the basil, run under cold water, then squeeze dry; transfer to a blender. Add 1/4 cup of the oil and puree; season with salt and pepper.
Preheat a grill pan. Toss the peaches with 1/2 tablespoon of the olive oil and season with salt and pepper. Grill over high heat, turning once, until the peaches are lightly browned, 3 minutes; let cool. Transfer the peaches to a bowl. Add the lemon juice and the remaining 1 tablespoon of oil and toss. Add the radicchio, red onion and feta, season with salt and pepper and toss.
Arrange the tomatoes on a platter and mound the peach-and-radicchio salad on top. Drizzle the salad with the basil oil and serve immediately.