Preheat the oven to 375 F.
Butter the bottom of the baking dish. Season chicken breasts from both sides with the Italian salad dressing mix. Place the chicken breasts, flat side down, into the greased baking dish and bake for 15-20 minutes at 375 F.
In the mean time, heat 1 tablespoon vegetable oil in a large skillet on medium heat. Add spinach and cook for only 1 or 2 minutes until it is heated through and starts to wilt. Remove from heat. Add minced garlic and half and half. Bring to boil. Add shredded mozzarella cheese and keep stirring, on high heat, until mozzarella cheese starts to melt - about 30 seconds. Reduce heat to simmer and keep stirring until you have a nice, smooth creamed spinach - about 30 seconds or 1 more minutes. The creamed spinach should be pretty thick in texture, not watery. If watery, bring to boil again and cook off extra liquid, constantly stirring. Season with salt. Remove from heat.
Remove the baking pan with chicken breasts from the oven (you baked them for 15-20 minutes). Top each chicken breast with creamed spinach, sun-dried tomatoes (drained from oil and chopped into smaller bites), chopped cooked bacon, and broken slices of pepper jack cheese. Bake in the oven, uncovered for 15-20 more minutes, until the chicken is completely cooked through, no longer pink in the center, and the juices run clear.