Heat the oven to 350ºF.

• Pat the pork dry with a paper towel; season with salt, pepper, and as much harissa powder as you like.

Let stand while you prepare the hazelnuts.

On a sheet pan, spread the hazelnuts in an even layer. Toast in the oven until lightly browned and fragrant, 8 to 10 minutes. Transfer to a cutting board to cool, then coarsely chop.
While the hazelnuts toast, start the peach-tomato salad.

• Cut away the cores from the tomatoes; cut the tomatoes into ½-inch-wide wedges.
• Trim the root ends from the scallions; thinly slice the scallions on the diagonal.
• Zest and juice the lemon, keeping the zest and juice separate.

In a medium bowl, stir together the tomatoes, scallions, lemon zest, 1 tablespoon lemon juice, balsamic vinegar, and 1 to 2 tablespoons oil. Season to taste with salt.
Let stand while you prepare the pork and peaches.

• Cut the peaches in half and remove the pits; cut the fruit into ½-inch-thick wedges.

In a large frying pan over medium-high heat, warm 1 tablespoon oil until hot but not smoking. Add the pork and cook, turning frequently, until browned but still faintly pink within, 8 to 10 minutes. Transfer to a cutting board to rest for 5 minutes, then cut the pork across the grain into ½-inch-thick slices. Do not clean the pan.
In the same pan used for the pork, add the peaches and cook, stirring once or twice, until just tender and heated through, 2 to 3 minutes.
While the peaches cook, chop the parsley and mint.

• Strip the parsley and mint leaves from the stems; coarsely chop the leaves.

Transfer the warm peaches to the bowl with the tomato mixture. Add the hazelnuts, parsley, and mint and stir to combine.

Transfer the pork to individual plates and sprinkle with the sumac. Serve with the peach-tomato salad.