Dry toasties happen when the filling is all fat and no contrast. The fix is moisture and acidity. Butter the outside for crispness, then add a condiment inside that brings tang.
Cheese toasties love sweet brown pickle. Ham toasties love golden piccalilli because it spreads neatly. If you want heat, chilli piccalilli brings mustard bite. For a brighter finish, a sweet and sour pickle like achar gives crunch and acidity.
A toastie is comfort food. Pickles make it taste less beige and more like you chose it.