Meal time

Hi, can I have some insight on how should I deal with a 5y.o diagnosed with ADHD and ASD who constantly gets up from the table and gets distracted with every little thing around him, taking him extremely long to finish a meal. I know he can focus on things when he wants to so how can I get him to eat his food and be dome with his meal quickly with the rest of the family. Please help me to fix my own mess.