Place chicken in a gallon-size ziploc. Put onion on top. In a quart-size ziploc, place dried herbs, garlic cloves, vinegar and tomatoes. Put quart-size ziploc inside gallon ziploc. Place in freezer. The day before you want to cook, place in refrigerator to thaw. On the day you want to cook, pour the olive oil on bottom of slow cooker. Add chicken breasts and onion. Sprinkle with salt and pepper. Dump contents of quart-size ziploc on top.
Cook on high 4 hours, serve over angel hair pasta or whole wheat egg noodles.