Preheat the oven to 400°F and line a baking sheet with parchment.
Drizzle the sweet potato halves with olive oil, rubbing it in with your hands to coat, and season with salt. Place cut-side down on the baking sheet.
Roast for 30 to 40 minutes, until a knife slides into the thickest part with no resistance and the cut side is deeply golden.
Meanwhile, add the cabbage, cilantro leaves, and green onions to a bowl. Squeeze over the lime juice, then add the olive oil, maple syrup, and salt. Toss and set aside.
Heat a skillet over medium and brown the ground beef, breaking it up as it cooks, 7 to 8 minutes.
Add the seasonings and the chopped cilantro stems. Cook 2 minutes more, stirring, until fragrant.
Spoon off most of the fat, add the water, and scrape up the browned bits from the bottom of the pan. Cook about 1 minute, until the beef is glossy and coated.
Add two sweet potato halves to each bowl, top with the beef, and finish with the slaw. Crumble over the queso fresco if using and serve with lime wedges.