Position a rack 6 inches from the broiler element and heat the broiler on high. Arrange the pancetta on a large rimmed baking sheet and broil until crisp, 2 to 3 minutes. Transfer to a paper towel-lined plate.
Halve the baguette lengthwise. Put the bread cut side up on the oven rack and broil until golden, about 1 minute.
Spread the mayonnaise on the bottom half of the baguette. Lay the tomato slices over the bread and season lightly with salt and pepper. Top with the peach slices, pancetta, and then the lettuce leaves. Replace the top half of the bread, cut the sandwich into 4 pieces, and serve.
Serve with a simple side of Pan-Seared Summer Squash with Crisp Rosemary.
nutrition information (per serving):
Photo: Scott Phillips