In a large resealable plastic bag, combine chicken, soy sauce, brown sugar, ginger, and garlic. Seal bag, tossing gently to combine. Refrigerate for 2 hours.
Preheat grill to high heat (400° to 450°). Place a 12-inch cast-iron skillet on grill to heat for 15 minutes. Spray skillet with nonflammable cooking spray.
Add peaches and tomatoes to skillet; cook, stirring occasionally, until just lightly charred, 1 to 2 minutes. In a medium bowl, stir together peaches, tomatoes, onion, cilantro, oil, lemon juice, honey, and salt until well combined.
Drain chicken, discarding marinade. Add chicken to skillet skin side down; cook until a meat thermometer inserted in thickest portion registers 165°, about 5 minutes per side. Return to skillet, and serve immediately with peach mixture.
Recipe by Southern Cast Iron at https://southerncastiron.com/chicken-thighs-peaches-green-tomatoes/