Heat the oven to 400ºF. Combine the gochujang, soy sauce, ginger, and 3 tablespoons of oil in a medium bowl or resealable bag. Add the sweet potatoes, red potatoes, green beans and peaches, and toss to coat with glaze. Lightly season with kosher salt and transfer to a rimmed baking sheet.
Season the ham steak halves with salt and black pepper, and toss to coat with whatever is left of the glaze in the bowl.
Arrange the ham steak halves between the vegetables on the baking sheet and roast until vegetables are tender, about 40-45 minutes.
While roasting, thinly slice the scallions. Using a sharp knife or mandolin, cut the radishes into thin rounds. In a small bowl, toss the sliced scallions and radishes with lemon juice and sesame oil. Season to taste with salt and set aside to marinate.
Top the roasted ham steaks and vegetables with the scallion-radish mix and transfer to serving plates.