Heat the avocado oil over medium-high heat in a large thick-bottomed pot or a 12-inch skillet (a wok or cast-iron skillet also works).
Add the yellow onion and sauté, stirring occasionally, until the onion begins to sweat, about 3 minutes.
Add the thinly sliced cabbage and sea salt, stir to combine, then cover the pot or skillet and cook for 3 to 5 minutes until the cabbage begins to soften; remove the lid and push the cabbage to one side of the pan to make room for the beef.
Place the ground beef on the open surface of the pan and use a spatula or wooden spoon to break it up; brown the beef for 3 to 5 minutes until chopped into small bits, then mix it into the cabbage.
Add the chopped red bell pepper and minced garlic and stir, then add the chili powder and tomato sauce and stir everything until well combined.
Add the baby spinach, cover the pot for 3 to 4 minutes to wilt the spinach, then uncover and give everything a big stir to combine.
Assemble bowls with the beef and cabbage mixture and top as desired with grated cheese, green onions, avocado, salsa, and sour cream; serve with white or brown rice or cauliflower rice and lime wedges.