Step 1 - cut the fat off the chicken and slice it into about ½-inch thick pieces. Season with salt and pepper and preheat your oven to 350 degrees Fahrenheit.
Step 2 - Heat a cast-iron skillet or a dutch oven to medium-high heat and add in your butter and 1 tbsp. olive oil. Add in your chicken and brown both sides. The chicken will finish cooking at a later step. Repeat with remaining chicken. Remove from the pan and plate to the side.
Step 3 - Add second tbsp. of olive oil and add the onions, peppers, and garlic to the same pan and cook for one minute scraping up any brown bits . Add in the thyme, basil, oregano, salt, and pepper.
Step 5 - Return the chicken to the pan, but do not submerge in the sauce. Place in oven and cook for 1 hour.
Step 6 - Meanwhile, to make the cauliflower mash - bring a pot of salted water to a boil. Add the cauliflower and turn the heat down to med-low. Cook covered for 15 minutes or until cauliflower is soft and tender. When it is done, remove from heat and drain in a colander.
Step 7 - Put the cooked cauliflower into a large bowl and add the butter, milk, garlic powder and desired salt and pepper. I own a hand blender I got as a gift for my bridal shower. It is the best thing I own and I used it to mash the cauliflower. If you do not own one you can pour cauliflower into a blender or food processor and blend until smooth. Step 8 - Once chicken is done cooking remove the pan from the oven. Take the chicken and veggies out of the pan and put them on a separate plate. Use a slotted spoon to remove veggies but leave the sauce in the pan.
Step 9 - Turn the stove on medium-high heat and place the pan with the sauce back on the stove. Add the mushrooms and cook until tender; about 5 minutes. Then add the spinach and cook until wilted; about 3 minutes.
Step 10 - To plate; spoon the cauliflower mash onto the plate and then top it with the chicken and veggies then the sauce poured over top! If desired, top with grated parmesan and fresh chopped parsley.