Melt the coconut oil in a large pot over medium heat, and sauté the onion, pepper, and pepperoni (if using) until tender, about 8 minutes.
Add in the shredded kale, cabbage, tomato paste, salt, and oregano, and sauté until the greens begin to wilt. Add the water to help prevent sticking, and cover the pot to let the veggies cook until tender, about 8 to 10 minutes.
Remove the lid and stir, making sure all the liquid has evaporated. Adjust any seasonings to taste and serve warm, with a sprinkling of feta over the top, if desired.