Combine peas, basil, garlic, and pistachios in a food processor. Process until peas are completely broken down. Add lemon juice and salt. Process while slowly adding olive oil to the mix, until it is all added. Finally, add the parmesan cheese and process. Adjust with more olive oil if necessary.
Preheat the oven to 375℉. Butterfly the chicken, in thirds. Slice the chicken thin like making cutlets but leave them connected at the edge. There should be two slices made and two places in the chicken breast to stuff.
Slather both pockets of the chicken in pesto and then stuff it with mozzarella. Fold the chicken back over and salt and pepper both sides of it.
Heat a cast iron skillet over medium-high heat. Add avocado oil or extra virgin olive oil. Place both chicken breasts on the cast iron. Sear each side for 3 minutes. Transfer into the oven and bake for 15 minutes or until chicken reaches 165℉.
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Notes
The complete recipe for Pea Pesto is easy and freezes well.
The key to cooking moist stuffed chicken is always using an instant-read thermometer. The fact of the matter is, every oven is different and every piece of chicken is different. If we all cook it for the same amount of time, some are guaranteed to be overcooked. Doing a temperature read is the safest and best way to cook your chicken to perfection.
When searing the chicken, wait until the pan is hot and barely starts to smoke. Then place the chicken on the pan and sear for 3 minutes undisturbed before flipping.
For this recipe, I originally tried to butterfly the chicken with just one slice like you normally would. We agreed the pesto-to-chicken ratio was off. If I was stuffing it with vegetables that would be one thing but a layer of cheese and pesto can be very thin. This was much better when we sliced two pockets to stuff.