That stew does sound rather plain. I'd add stuff like leeks and also just more vegetables of your choosing. A mirepoix, spinach, kale, peas, whatever vegetables you like. I'd also add some stock cubes. I don't think ground meat makes very good stock, so it would benefit from stock cubes/powder. It's just cheaper to bulk things out with vegetables and carbs.

As for making you feel full for longer, generally fat makes you feel full for longer, so you could try getting ground meat with higher % fat (sticking to your ingredients) or just adding maybe some olive oil or butter to the stew. It is extra calories which I guess might make you gain weight, but calories are energy and excess energy becomes fat (stored energy), so your two stated goals of not gaining weight and having enough energy are at odds—not irreconcilable, but it'd be a balancing act.