Preheat the oven to 400F. In a large cast-iron skillet (or on a parchment lined baking sheet), add the sweet potatoes. Drizzle 1 tablespoon oil and sprinkle ¼ teaspoon salt all over. Use your hands to rub the oil and the salt all over the sweet potatoes. Transfer to the oven for 30-50 minutes more, or until tender (this depends greatly on the size of your sweet potatoes)..
In a separate large skillet over medium heat, add the remaining 2 tablespoons olive oil, veggies, and ½ teaspoon salt. Cook until the veggies are tender, stirring occasionally, about 5 minutes. Add the oregano, garlic, red pepper flakes (if using), and tomato paste and cook for 1 minute, stirring often. Stir in the water, beans, and remaining 1 ¼ teaspoon salt. Cook for 30 seconds, stirring often, or until the water thickens into more of a sauce.
Once sweet potatoes are cooked through, flip them over (cut-side-up) and use a fork to mix/mash the center to make room for the filling. Sprinkle a bit of salt on top of each sweet potato. Add the filling to each sweet potato, then top with a generous amount of cheese. Bake for 5 more minutes, or until the cheese is melted.
Serve topped with parsley (if using) and with a simple side salad or slaw (it’s nice to have something crunchy and bright on the side since the potato and beans are a bit mushy).