Spray the crockpot with cooking spray. Add diced potatoes & onions to the bottom.
Slice the chicken breasts into halves or thirds, depending on their size. Add them in one layer evenly over the potatoes & onions. Nestle the rosemary down in between two pieces of chicken in the center of the pot.
Pour the chicken stock into the pot. Sprinkle the whole dish with the seasoning. Add the lemon peel evenly over the chicken. Cover. Cook on low for 3 hours.
When cooking time is up, discard the rosemary & lemon peel. Transfer the chicken to a serving platter. Add the potato-onion mixture to the platter. Sprinkle shredded parmesan over everything. Cover platter with foil to melt the cheese.
Ladle 2 spoonfuls of broth from the crockpot into a small bowl. Add the basil pesto to the broth & whisk until combined. Pour over the chicken & serve remainder with the meal.
