Heat large skillet over high heat. Add butter or lard. Add chopped onions and 1 teaspoon sea salt. Saute over medium-high heat for 5 minutes. Cover and reduce heat to medium for 5 additional minutes. Stir in oregano (or rosemary) and turn off heat. Allow to cool slightly while you proceed with recipe.
Line a LARGE loaf pan with parchment paper. Preheat the oven to 350 degrees Fahrenheit. Place large cookie sheet on oven shelf (to catch any drips from meatloaf as it bakes.)
In small bowl sift together cassava flour and baking soda. Set aside.
Drain liquid from jarred roasted peppers. Place them on a cutting board and slice them into 1/2" strips. Set aside.
Into a large food processor fitted with a metal blade add the following in this order: 3 eggs, fresh mint, garlic, essential oil, ground beef (broken into smaller chunks), remaining 2 teaspoons sea salt, and cream. Top with cooling onions. Sprinkle cassava flour (or psyllium) over food processor ingredients. Pulse mixture about 5 times, to mostly distribute. Pulse a bit more if needed. (Don't over mix.) {You can also mince the fresh mint and mix all of this with your hands in a large bowl, which is the old-fashioned way of making meatloaf. That's a great option and will just turn out a slightly different texture than using a food processor.}
Remove lid. Add frozen spinach and feta, broken into both medium size and small chunks. Pulse again 3-4 times. At this point the food processor is very full. Use a wooden spatula to push some of the feta and spinach down into the meat mixture, but don't over mix. {Or if using your hands and a bowl, mix in spinach and feta manually.}
Scoop/pour and spread meat mixture into loaf pan, evenly distributing any larger chunks of feta or spinach. Shape the top so it's slightly mounded in the center.
Lay pepper strips across the top of meatloaf decoratively. Press them in slightly.
Place meatloaf on cookie sheet in preheated oven. Bake 1 hour and 10 minutes, if using large loaf pan. Remove and allow to cool for 15 minutes before slicing.
Serve with Greek olives, cucumbers and whatever else you love from this region: probiotic sour cream/thick yogurt, fresh lemon wedges, tomatoes if in season, a big green salad with red onions and olive oil, capers, figs, oranges etc.