Prepare marinade by whisking together olive oil, lemon juice, lemon zest, dijon mustard, minced garlic, chopped basil, kosher salt and black pepper. Whisk until evenly mixed and emulsified.
Toss chicken thighs in the marinade in a mixing bowl. Cover the bowl and place in the fridge to marinate for at least one hour or up to 4 hours.
To cook on the stovetop: heat a skillet over medium heat. Place a few chicken thighs in the pan at a time - cooking in batches to make sure not to overcrowd the pan. Cook for 4 minutes, flip and cook another 4 minutes, flip cook 2 minutes and check internal temp. If not yet 165F, flip again and cook until internal temperature reaches 165F.
To cook on the grill: Clean grill grates and heat grill over high heat. When the grill reaches 500F, reduce heat to medium. Place chicken thighs on the grill grates time. Cook for 4 minutes, flip and cook another 4 minutes and check internal temp. If not yet 165F, flip again and cook until internal temperature reaches 165F.
Allow chicken to rest for at least 5 minutes before eating.
If making for meal prep, allow chicken to cool completely before transferring to an airtight container.
Notes
you can use chicken breasts instead of chicken thighs - I recommend cutting each chicken breast into 2 thinner fillets
Do not marinate for longer than 4 hours because the lemon juice can start to change the texture of the chicken. If you want to marinate longer than 4 hours, omit the lemon juice and just use the lemon zest.