Cut a horizontal slit in the center of the chicken to form a pocket.
Combine the oregano, thyme, salt, and pepper in a small bowl and set aside.
Heat 1 tablespoon of the avocado oil in a skillet over medium high heat. Add the onion and cook for 4 minutes. Add the garlic and spinach and cook until the spinach wilts, about 2 minutes.
Add the lemon juice and zest to the pan and cook for 1 more minute.
Transfer to a bowl and stir in the ricotta and feta.
Stuff the chicken pockets with the cheese mixture and secure with toothpicks. Sprinkle with seasoning.
Heat the remaining tablespoon of oil in a large skillet over medium-high heat.
Add the chicken and cook until golden brown and cooked through, about 5 to 7 minutes per side.
When the internal temperature of the chicken reaches 160° F, remove from the pan and tent with foil.