In a large frying pan or wok, heat avocado oil over a medium flame, but not smoking.
Add chicken and cook, stirring continuously until the chicken is tender, about three-four minutes. Remove the chicken to a plate and set aside.
Then stir fry the sliced peppers along with garlic, crushed red pepper, oregano,salt, and pepper.
When the peppers are just cooked, 1-2 minutes, add butter and stir until it melts.
Finally, toss the chicken back in the wok with the spinach and keep the ingredients moving constantly by stirring with a wooden spoon for a minute or two. You'll find that the spinach wilts as the flavors merge.
Turn off the flame and add Parmesan cheese, parsley, and lemon juice. Toss and serve.