Some low growing shrubs and bushes are..
Hostas.
Heather.
Heuchera.
Lady's Mantle.
A few ground covers that might be good..
Ajuga
Alyssum
Trailing Campanula.
Thyme.
For even more ideas you can check out this website https://www.thetortoisetable.org.uk/index.php#.WtJY9OBlA0M
Hostas grow best in shade. They are usually a well liked food source for torts and may even need some protection from a tort to prevent it from being eaten to the ground.
Heather, Heuchera, and Lady's Mantle are safe for a tort to eat but usually not liked. A smaller tort could easily crawl under the leaves to hide.
Of course you should not feed your tort recently bought plants because of the risk of pesticides and fertilizers. An absolute minimum of 6 months before feeding nursery grown plants, unless you know that the plants were grown chemical free.
Another option is to grow your plants from seeds.
To give better advice and recommendations it would be good to know the species of tort and what area you live in.