Place chicken thighs in a food storage container and squeeze the ranch salad dressing over the chicken, turn to coat the chicken in the ranch dressing. Place the lid on the container and place in the refrigerator and allow to marinate for at least 2 hours.
Dice the potatoes, onions and cooked bacon into bite sized pieces.
In a large skillet on the stove-top over medium-high heat add the olive oil and let it get hot. Add the chopped potatoes, onions and bacon to the pan and cook for about 10 to 15 minutes until the potatoes are slightly browned and the onions are translucent.
Add the potato and onion mixture into the bottom of a 6 quart or larger slow cooker and spread it out evenly.
Sprinkle half of rosemary and garlic seasoning on top of the potatoes.
Sprinkle the potatoes with a thin layer of the 3 cheese blend.
Place each ranch covered chicken onto the potatoes. Discarding the remaining ranch dressing marinade.
Sprinkle again with the remaining half of the rosemary and garlic seasoning, paprika, salt and pepper. Then sprinkle a thicker layer of shredded 3 cheese blend.
Cover and cook on LOW for 7 to 8 hours or 4 to 5 hours on HIGH or until the internal temperature of the chicken registers 165°F on a instant read meat thermometer.
Once you've reached that temperature add another layer of cheese and small chopped tomatoes and continue cooking for 20 to 30 minutes more on LOW.