Depending on the taste you want, you could try a couple of different recipes.

There is an Antipasto Relish from Ball's website.

I make an Australian style tomato relish. I stated in that post it wasn't a USDA approved recipe, but the consensus was it's pretty low-risk.

You could always make Chili Sauce.

Maybe look those recipes over, and describe the flavor you are looking for. A traditional relish uses firmer ingredients like cucumbers, green tomatoes, etc. so I'm thinking the finely diced ripe tomatoes wouldn't give you the same texture and would cook away into "sauce" anyway.