Place peaches, tomatoes, red pepper and onion halves skin side down on a sheet pan and place in oven until slightly charred, about 7-10 minutes. Remove from heat and let cool.
Prepare boiling water canner. Heat jars in simmering water until ready to use, do not boil. Wash lids in warm soapy water and set aside with bands.
Dice peaches and tomatoes, leaving charred skin on. Dice red onion halves and red pepper. Combine everything up to the cilantro in a 4 quart saucepan. Bring to a simmer over medium heat, stirring frequently. Simmer until peaches have softened slightly and flavors have combined, about 10 minutes. Stir in cilantro.
Ladle hot salsa into a hot jar leaving a ½ inch headspace. Remove air bubbles. Wipe jar rim. Center lid on jar and apply band, adjust to fingertip tight. Place jar in boiling water canner. Repeat until all jars are filled.
Process jars 20 minutes, (adjusting for altitude if above 1,000 feet). Turn off heat, remove lid, let jars stand 5 minutes. Remove jars and cool 12-24 hours. Check lids for seal, they should not flex when center is pressed.
Notes
This is a certified BALL® Canning recipe, that has been tested and approved. It was originally posted here.