Danelle,
Stitch is only at the
'Ohana breakfast. So if you love Stitch (and who doesn't?!?), breakfast it is. Also, for your information, 'Ohana is not open for lunch, and at dinner it is not a character experience.
As for other meals at the Polynesian, there is the famous Disney Spirit of Aloha luau (dinner only), and Kona Cafe. Kona is a often overlooked restaurant, but is it GREAT at breakfast, lunch, and dinner! The food and service are great, and offers a lot of variety. There is even an adjacent sushi bar, which makes for a nice pre-dinner appetizer! Oh, and there is also the counter service at Captain Cook's for that quicker meal need.
Write me back if you have any follow-up questions! I am glad to share more about these and other dining options!
Have a magical (and delicious) vacation!